Well for the majority of the mandates if they were treated as colonies it likely wouldn't make much of a difference in the long run at least for the British mandates since the birth of the Commonwealth in the mid 1920s essentially laid the groundwork for a transition to independence for all the colonies eventually. India obtaining dominion status after the war basically guarantees the same for the West Indies, Malaysia and the African colonies down the road. In addition Mandatory Iraq had gained formal independence in 1932; so this also sets a precedent for the other British mandates although Iraq, like Syria (including Lebanon initially) and Palestine (including Transjordan initially) were Class A mandates which were explicitly recognized as being at "a stage of development" that they could exist as independent nations. Whereas Class B mandates (like Cameroon and Tanganyika) were treated more like regular colonies, and Class C mandates (SW Africa, South Seas Islands Mandate, New Guinea, Nauru and Samoa) were considered "best administered" under the laws of the Mandatory powers as "integral portions of [their] territory".
I'm still wondering if we aren't viewing the disposal of the mandates through an OTL lens with the idea that all the mandates were legally required to become independent (when essentially only Class A mandates were recognized as such). If that was the case, then the OTL 1946 French Union attempt would have been illegal since it provided for France, France's various colonies as well as the mandates/trust territories (and these were formerly Class B mandates) to be fully assimilated into a single French state. Even the trust territories themselves after the UN was founded did not automatically envision that decolonization would lead to independence as we saw with the Northern Marianas which voted to become a territory of the United States.
Additionally in TTL the global landscape is vastly different from OTL. In OTL we had two superpowers after the end of WWII which were explicitly anti-colonial in character (one a former colony, the United States; the other a communist state, the Soviet Union). All other great powers that had been explicitly colonial in character had either been defeated (Italy, Japan) and divested of their overseas holdings or were victorious but massively weakened (France, the United Kingdom, the Netherlands, Denmark, Belgium) by six years of brutal warfare and in many cases foreign (usually German) occupation. The only colonial powers that weren't really impacted by the war were Spain and Portugal and even here the environment in which they found themselves in post-1945 was one where colonialism was being pushed out as the USSR and US on principle opposed it and also supported various independence movements to basically outflank each other in the growing Cold War. The system that was set up (the UN) was also explicitly against indefinite colonialism on principle.
Here we literally have none of that. The Soviet Union remains mostly isolated from global influence except perhaps in supporting Nationalist China at points. Italy, Japan, the Netherlands, Denmark, Belgium, France and the UK have not been diminished in power as in OTL by being weakened by Germany's war on them. The US has not been involved in the war at all. I would imagine decolonization would come for quite a few territories but that it would not necessarily be like OTL. Firstly the Philippines would likely become independent in 1945 (unless we get a major Japanese-American War) and many British colonies would likely be granted dominion status. However in the context of TTL 1943 onwards these events would likely look different than OTL post-1945; the Philippines would probably be a bit closer to early 1900s Cuba than OTL 1946 Philippines insofar as they would be independent but the US would still have massive sway and aspects of Filipino independence might be proscribed/restricted. The British dominions would probably more resemble the pre-1939 status than the OTL post-1946 status (in the informal terms of being more closely knit). India's independence as a dominion will shake things up as I imagine that India will eventually want to become a republic and perhaps something like the 1949 London Declaration will be adopted. In fact, assuming that the Commonwealth Prime Ministers' Conferences are still held, then the first meeting is likely to be a post war meeting in 1944 at which perhaps the issue of Ireland's status might get a first full airing (with Ireland already considering itself a republic that was only associated with the Commonwealth; while the other states considered it a dominion still). With de Valera still as Taoiseach it might be possible that the framework of the 1937 Irish Constitution becomes the basis for de Valera to propose (in 1946) something similar to the Nehru's eventual 3-point programme of 1949 that laid the foundation for the 1949 London Declaration that allowed republics to remain members of the Commonwealth. Thus we might get Irish membership of the Commonwealth explicitly as a republic (at least until Costello succeeds him and probably takes Ireland out of the Commonwealth until de Valera comes back in in the 1950s).
As things seem to stand in TTL 1943, independence for most countries as we recognize it today would be some ways off. Instead many countries might look more like "free associated states" at best or protectorates at worst.
When you say that "prior to that, there was a sense that SW Africa would get its independence eventually" would this include the period 1922-1949? I ask because I want to be sure we aren't viewing this from the OTL post-1945 lens. If the sense was there from say 1933 for example that SW Africa would eventually get its independence then this sets things up for SW African organizations to ally with the ANC and for Namibian independence to become a part of the struggle against white minority rule (if not Apartheid as well since as you tantalizingly discussed, outright Apartheid might be avoided though some Jim Crow analogue may not be - in which case one might see an even earlier Namibian independence if the Jim Crow analogue ends in South Africa at around the same time as Jim Crow ended in the US in the 1960s). However, if the sense of SW African independence being inevitable arose in 1945 (and not before) due in part to the sea change in the wider world with:
1. the establishment of the UN
2. various declarations associated and integral to the UN from the Atlantic Charter and the UN Charter (note that pdf27's Placentia Bay Charter is similar to OTL's Atlantic Charter but unlike OTL's Atlantic Charter it does not advocate for self-determination for all peoples by saying in the third point that "they respect the right of all peoples to choose the form of government under which they will live") including Chapter XI of the UN Charter
3. Two superpowers that pushed for the independence of colonial territories
then are we sure that the same sense will arise in TTL post-1943 without any of these (and other) factors? That the various SW African groups won't instead be like various groups in the original South Africa and start fighting for equality within South Africa?
