*all of these actors explicitly noted the end of slavery in the United States as a principal motivating factor.* [my emphasis--DT]
Though, given that the Brazilian move failed, it seems the motivating factor provided by the Civil War was relatively small and, by extension, would not have been difficult or impossible to replace. More fundamental, slower-moving changes than the Civil War helped push Brazil towards abolition. The breakdown of the coercive system during the Paraguayan war, allowing slaves to escape, find shelter in quilombos or join the army; the rise in coffee exports, which oriented Brazil's economy to the international market; the growth of new-money coffee planters and the development of white-collar urban workers; the stimulation of manufacturing in the Paraguayan war and its continued growth after the war; foreign immigration and the changes in the labour market which it caused: none of these factors were the result of the Civil War, and all of them were critical to ensuring that the move towards emancipation which was stillborn in 1865 came to fruition in 1888.
We should probably be unsurprised if a book entitled
Transnational Meanings of the American Civil War plays up the role of the Civil War abroad, given how short it might be if it didn't do so. We should also bear in mind that this is an American book dealing with a key story in the national history which took place less than 150 years ago and with significant contemporary ramifications: avoiding at least a degree of unconscious bias under these circumstances is more or less impossible. In more general works dealing specifically with Brazilian emancipation, different views of the motivations behind abolition are given:
The increasing demand for labor in an expanding coffee economy and the rise of urban groups dissatisfied with slavery as a system made abolition a necessity. Why then, we may ask, were the first steps toward abolition taken in the late 1860s and early 1870s, before either of these forces could be considered very strong? And why was the African slave trade prohibited as early as 1850? The answer to both these questions is to be found in the pressure applied by the British. British efforts to destroy the slave trade have been much discussed and need not detain us here... It is less well known that Britain continued to put pressure on the government of Pedro II in the 1850s and 1860s until Brazil itself gave evidence of a firm commitment to end slavery. Whereas the law freeing those children of slaves born after September 28, 1871, is usually considered the first evidence of an abolitionist campaign, it was really the conclusion of the British phase of the story which had begun forty years earlier. (Richard Graham, 'Causes for the Abolition of Negro Slavery in Brazil: An Interpretive Essay,'
The Hispanic American Historical Review, Vol. 46, No. 2 [May 1966] pp. 129-130)
Indeed, there are suggestions that the Civil War may have delayed Brazilian abolition:
The U.S. model of abolition had multiple meanings for Brazilians playing a very different role in each of the phases in which the Brazilian abolitionism unfolded, the Paraguayan War being the internal element which propelled the shift in the Brazilian representation of the United States from one stage to the other. In the first phase, we found that the U.S. path to abolition was seen as a dramatic event which brought the case of the United States to the fore as a negative example and thus as a model to be avoided. The war whereby slavery was brought to an end had been too appalling in its costs and too unpredictable in its consequences which were likely, moreover, to cause further social hatred and unrest. (Natalia Bas, 'Brazilian images of the United States, 1861-1898: A working version of modernity?' [unpub. PhD thesis, University College London, 2012] pp.54-5)
To nuance the argument further, Seymour Drescher saw two models of abolitionism. One was the Anglo-American model, slow moving but employing broad popular appeal to secure abolition; the second was the Continental model, focused on central government and negotiations between key stakeholders (Seymour Drescher, 'Brazilian Abolition in Comparative Perspective,'
The Hispanic American Historical Review, Vol. 68, No. 3 [August 1988], p.441). He suggested that Brazil's moves towards emancipation followed the second model until the 1860s:
"Great Britain's role was preponderant in linking the achievement of independence with formal abolition treaties. Britain also intervened in Brazilian domestic slavery over emancipado issues... Even more blatantly than in the European context, moreover, the British government "colonised" abolitionism in Brazil through secret subsidies and covert agents." (p.443)
What I'm suggesting is that Brazil either continues to follow the Continental path or creates a hybrid between the two. The compensated emancipation and period of indenture which I suggested were a hallmark of this model, based as it was on securing the acquiescence of the slaveholders.
There's another reason I find the argument that Confederate victory would have little effect on Brazilian emancipation compelling: many of the factors you listed as being critical to its success to support your argument don't actually change in the event of Southern independence. For instance:
"With Washington DC no longer acting internationally in the interests of slaveholders, the United States finally cooperated with Great Britain in its decades-long effort to abolish the transatlantic slave trade.
This paragraph conflates slavery and the slave trade, but I'll deal purely with the latter here. After February 1862, when the US conceded the right of search to the British, slave ships can no longer escape justice by hoisting a Union flag. The Confederacy has outlawed the slave trade, and has little interest in provoking the British by refusing them the right of search. If Britain doesn't secure a clause in the peace treaty providing for mutual rights of search, or sign a separate treaty with the South after the war, the government may simply conclude that it has the right to search Confederate ships because the South's independence was not established at the time the Union signed the treaty. Palmerston's treatment of Brazilian and Portuguese slave ships provides a similar previous example of this.
"In the urban centers of Brazil, which had grown in wealth and sophistication over the years, *the advance of international abolitionism inspired many.*
Note that this says
international abolitionism: I hope Rugemer wasn't thinking solely of the Civil War, because as it happens Brazil looks as much to Europe as to America in this period. Moreover, international abolitionism will still unquestionably be advancing despite Confederate independence- the very result that most British abolitionists expected.
"So attractive to the English was the vision of an emancipated North achieving a moral renaissance by sloughing off the South, and then steadily growing in strength and excellence at the expense of an independent but decadent rival, that it became something of a cliché in the next year or so." (D.P. Crook, 'Portents of War: English Opinion on Secession,'
Journal of American Studies, vol. 4 p. 2 [February 1971] p.178).
As the North emancipates its slaves a few years after the war; as the North inevitably grows and the South stagnates; as British and American government officials and private activists highlight this increasing disparity; as the Union seeks engagement with the wider world in the interest of checking its new rival on the American continent, finding abolitionism a useful tool to build these links, the cause of emancipation will advance.