It was pretty hard to see the development of specific aspects as Weimar World is largely written like a CV and three fourths of the timeline discussion deals with the first thirty years (or maybe even two thirds with the first twenty years). That split you talk of only reminds me of the New Britain timeline, but that larger home rule and a shift of power towards a bigger country within the structure becomes inevitable is out of debate for me. If you don't want the British Empire to become a Commonwealth as untight as that of OTL but want to have that devolution spirit intact, you may even think of handing over colonies to locally near dominions. The Australian Commonwealth received Papua New Guniea from the British metropole virtually after its foundation. You may do the same to most of Southern Africa as of the late 20th century, at least receiving Namibia and Rhodesia. A racially desegregated by the late 1970s.
ATL Japan = OTL Serbia
ATL South Korea = OTL Kosovo (or „North Albania“)
ATL North Korea = OTL Albania (or „South Albania“)
The relatively thin 1990's deal, among other things, about protests for Choson independence. Koreans of the South want to get rid of the Japanese, but reunification with the North is somehow disaccelerated due to human rights violations up there, at least in public opinion. It might seem plausible that the Americans would have forced the Japanese to grant substantial autonomy to their Korean holdings after the Pacific War if Japan really would have been allowed to keep it. I might see that at one point the people of the Choson province unilateraly declare their independence, just like Kosovo did from Serbia in OTL recently, though not with the same bloodbath.
I might even see less reluctancy from Japan to Choson recession ITTL than the reluctancy Serbia is showing to Cosovar secession IOTL, maybe because the Japanese sweared themselves to be an extremely civilized nation and want to literally save their face compared to the French who lived to see some kind of counter-secession with the French Union expelling them. And because Korea isn't the myth of a cradle of nation that Kosovo is to Serbia.
When the Choson province becomes independent, the old question of reuniting the two Koreas will be asked again. Reunification would be seen as an essentially good idea, but it's obvious that the fifty or maybe sixty years of division produced some kind of alienation which is at least as severe as that of the two Germanies IOTL, though that alienation among Koreans may not be that extreme ITTL as IOTL. And yes, this alienation IOTL also happened to the Albanian nation where Albania proper also has experienced decades of Stalinism. These parallels are absolutely deliberate.
The Med is a side arm of the Atlantic to me, north of Africa and therefore quite north of the Equator and any other thinkable line that could be thought of to be the dividing ling between a Northern and Southern. Even if you don't count the Arctic Ocean to be a marginal sea of the Atlantic, even having Russia in the NATO wouldn't make the name ridiculous as long as St. Petersburg remains Russian territory, though definitely being a borderline case.
BTW, as the 1960's show forms of economic co-operation among the NEA members, there might be different names for the defense pillar (the classic NEA) and the economic pillar (EEC or similar). As there already is a European Federation as of 2004 ITTL, that would match perfectly into the genuine pattern of European integration ITTL. OTL European Union has an even more incomprehensible pattern of pillars than the European Federation of Weimar World.
IIRC it's still the British and the French that rule the oil industry in Africa IOTL. Lowlands are in united Europe ITTL since the 1940's, though the Belgium story might still get fleshed out as the redeployment of LoN soldiers to Belgium only insufficiently explains what kind of place Belgium has become since the Bloody Monday in 1981. It's definitely a field to work on.
Fields to work on...
BTW, maps don't change at all after the 1990's.
