I think a 1890-1905 geopolitical axis&allies style game could be really cool. The pre-dreadnought era may fit A&A gameplay even better than the WW2 era. Ships moved alot slower. No ideologies just imperial ambition. Lots of interesting wars/battles in remote parts of the world like the Russo-Japanese War and Spanish-American War. It would be interesting to see how a Pacific war between Japan and the US would play out during this era. Until they were defeated in the first Sino-Japanese War(1895). China had a sizable modern navy so even they could be an important power. The total lack of ideologies means diplomacy should be a factor and players should be able to choose there friends and enemies( and make secret alliances). Nations who were allies in the Boxer Rebellion were fierce enemies just a few years later.
Yea and since everybody is doing it, nobody is really a “bad guy”, while Germany could still have its kaiser and nations like Spain and Ottomans would play their part.
All the technology could enter latter, plus as you mentioned a diplomatic phase would be a big part of the game, just like it was during the Moroccan crisis.
Plus as you also mentioned players would be free to make alliances in a free form game, like risk, except with AA style pieces.
You could even add in rules for fighting natives and looting Africa for gold or lumber to build ships. Zeppelins could transport supplies or just bomb the enemy ( this would be technology)
You could even make Mexico a minor power that could fight USA, or add Indian wars where units cost western developments for the US player.