A bit houseruley, but you could simply have the UK be a single economy but still two capitals, that way Japan could destroy Calcutta, then after the UK collects again, Germany finishes them off in London. You also need to make Moscow less attractive (G40 was created with the intention of Sea Lion and a more successful Burma campaign to be possible), so additional national objectives are needed for the USSR, with a combination of a means to make China more difficult for Japan, to prevent a Moscow-Rush or Dark Skies Strategy from always taking place.
Another thing is, the allies need simple and also possible to obtain victory conditions, so perhaps this:
Europe Victory: The Allies control 1 original European Axis Victory City; Calcutta and Sydney still under Allies Control
Pacific Victory: Japan controls no originally Pacific Allies Victory Cities; Moscow and London still under Allies Control