If Feng China decides that this is a good opportunity to complete Chinese unification, Russia will be fighting against the world's 2nd, 5th and 6th largest economies at the same time.
Feng China is almost guaranteed to be involved. However, it's 2nd, 5th and 6th versus 3rd and 4th - 1st being neutral - with all sides enjoying fairly major bunches of allies (Norden, Lithuania, Corea and the Beiqing for Russia - Siam, the Hermandad and probably Congo for the UPSA - Danubia and Poland for Germany - at least some Hanoverian kingdoms, Burma, and probably Venezuela, for the ENA - Feng China has its own sphere of allies/vassals to muster, so each of the five major belligerents so far can appeal to a network of supporst, sometimes a fairly major one, as the Hermandad, the Vitebsk bloc and the German-Polish-Danubian alliance show - I'd say the same applies to ENA and its Hanoverian bloc if there wasn't foreshadowing implying a rocky relationship between the Septentrians and the British. Note however that the Meridians keep treating the Hanoverian states as one, as they had done in previous confrontations. Oh, and the Mauré are also in the alliance with Germany, ENA and the Feng, although clearly more as cobelligerents (at best) than true allies. There appears to be little coordination between the largest powers on each side (Russia is not, it seems, talking with the UpSA about a joint strategy, nor, guess, are the ENA and the Germans doing that - although I expect the Meridians and the Siamese to talk each other, and likewise the Septentrians and the Feng).
The Armed Neutrals are also a power bloc not to be trifled with, France is a major power is Italy is also fairly strong overall. One wonders what are the Ottomans and the Persians up to, they're the only important powers we don't know about.