Pius was never in favour of Italian Risorgimento, although there were considerable hopes at first that he would be. He also initially opposed the Austrian and sent volunteers in the Italian national army, but he then recanted, which was logical for him (critically after radicals shot his finance minister Rossi) as he understood that Risorgimento, aside from the concept national unification, was largely a liberal and secular movement that, in many areas, opposed the Church and the traditional teachings she upheld. He could not head the Church as a conservative force (which it mostly was at the time) and be the standard bearer for a movement who at the very least aimed at upsetting one of the geopolitical cornerstones of the Old Order, that is, the staunchly Catholic Austrian Empire. He tried to ride the contradiction for a time, but when he had to choose, his choice was almost overdetermined.
This does not mean that under different circumstances, an Italian confederacy headed by the Pope was not a possible endgame of the Risorgimento. The idea was popular in some circles and many (as Gioberti whom you quoted) regarded it as the obvious way to square the circle: the contradiction between the need to preserve Papal authority and prestige and the will to unify Italy was there and was rather intractable as long as the Papacy insisted on its temporal power (which Pius IX was unflinhcing about) and a lot of people saw that as the way to solve the problem. This lot of people, however, never really included any Pope or cllose advisor of the Popes, and there were some serious problems abiut it. If it happened, however, the Pope would not rule Italy, that was never the plan. He would be the cerimonial president of some structure with any political power lying elsewhere.
Gioberti and his neo-Guelphs always represented a minority position: prior to the start of the insurrections in Italy and the Sardinian intervention, the most vocal component which demanded constitutional reforms and Italian unification was the republican one, loosely headed by Mazzini from exile, but again they were not likely to gain a majority even if they were certainly more numerous (and more likely to direct intervention) than the neo-Guelphs. IMHO, the majority of the liberal bourgeoisie and aristocracy was in favor of moderate reforms and the granting of a constitution but were certainly not so sanguine in terms of national unification: the best example among them was certainly Daniele Manin, who always argued for "reforms within the law" and even after the insurrection of Venice did not change his position substantially and certainly did not canvass for any national unification.
The enthusiasm for the election of Mastai Ferretti to the papal throne in 1846 owes more to the fact that his predecessor - Gregory XVI - was a reactionary of the deepest die (he was notorious for his opposition to railways, which he considered a diabolic invention, but also for the indiscriminate repressions of any agitation in the papal states and for the bad government of his states: Metternich himself is reported to have said that the restoration of the papal states was not one of the best decisions taken at the Congress of Vienna) and also that his major contender in the conclave of 1846 was card. Lambruschini, another notorious reactionary and filo-Austrian.
Another reason for which he was considered a liberal was his mediation during the insurrections of 1831 (while he was delegate for Spoleto and Rieti), when he convinced the papal troops not to fire against the insurgents, allowing them to leave Umbria with passports and some money (curiously, one of these insurgents was Louis Napoleon).
The first couple of years of his papacy seemed to confirm this fame of liberalism, and he was considered (without canvassing for it and most likely to his private chagrin) the emblem of Italian liberalism: in March 1848 he granted a constitution, and soon after allowed a division of papal troops and one of volunteers to march north after the insurrections of Milan and Venice (however these troops were forbidden to cross the Po river to engage Austrian troops). The writings of Gioberti date from this period, but Pius IX never took such a position as his own.
April 1848 was however the month when he realized the difficulty and the contradiction of his position (and it is quite certain that the college of cardinals was pretty vocal), and this culminated in his speech "Non Possumus", where he clearly stated that a pope could not wage war against a catholic monarch.
Unsurprisingly, the next 6 months the liberal reforms were slowly watered and the population of Rome became more and more restive, until on 15 November 1848 Pellegrino Rossi was assassinated and soon after the pope (in incognito during the night) left Rome for Gaeta: which clearly shows that his change of mind did not come up because of the assassination of Rossi, but rather his slow abandonment of liberal policies was the reasons for disorders and the assassination of his minister.
Over the rest of his life, he appears to have done his best to blot out his previous liberalism: the pope's executioners were always busy, a strong censorship was imposed, any liberal conspiracy or insurrection was dealt with very harshly (the worse episode was in 1859: the insurrection of Perugia was quashed in blood, and the city was given to the papal Swiss troops to sack for three days), the liberties given to the Jews in 1846 were revoked. His writing reflect well this U-turn: Quanta Cura, the Syllabus, Pastor Aeternus, the "non-expedit" speak very clearly and show the bitterness of a vindictive old man who had lost his temporal crown.
No surprise, anyway: theocracies never work well, irrespective of which particular God they claim to speak for.