You'd also have to tie intervention of different empires to hex flipping as well, despite what Chuut may claim, it's kinda obvious that any early era server is going to have Kzin outflipping Lyrans by a wide margin- so simply have rules that show if the Kzin (for example) advance X amount into Lyran space, then the Klingon Empire activates earlier.
<sigh> I guess the Klingons are too lazy to try to retake Lyraa
<snippy>
Ebb and flow with the entries of the various races at the proper times facilitating it.
The "ebb and flow" of the entries etc. all fit into the "historic accurateness" of the General War, as written by SVC & co.
Violate that, and then what do we do?
Consider:
Per "history": Early 4 powers was effectively Hydran/Klink & Kzin/Lyran. Upon the Klingons completing their "pasting" of the Hydrans, they invaded Kzin space, and the Kzin, unable to withstand the combined onslaught, prompted the desparation of the Hydran Expedition and resultant mobilization of the Feds.
However, if the Kzin stomped the Lyrans (entirely possible with your Kzin Success Scenerio), then the following questions need to be asked:
Would the Klingons even invade? And if they do, is it more an attempt to aid belegured Lyrans or an attempt to stomp the now-massive Kzin Hegemony before the Klinks are next on the invasion list?
Would the Hydrans feel the pressure to launch the Expedition, seeing their Kzin "allies" are actually capable of defending themselves? And without the Expedition, would the Feds begin to mobilize that early?
Would a Fed mobilization actually be geared as an anti-coalition move? Remembering the Man-Kzin war history, perhaps a Fed mobilization in that timeframe would instead be geared to defend Federation interests against the Kzin Hegemony, thereby blowing the Alliance apart before it even formed.
And if we were to enforce the "general war" dates irreguardless of the actual situation, the situation would be lopsided (Double strength Kzin, old-colony Hydrans and full Feds vs Klinks and what's left of the Lyrans.) Obviously, the situation will snowball (Lyran Empire genocided, then a 3 on 1 raping of the Klingons) into a no-questions asked Alliance victory. And we all know how played a snowball server actually is...
Prior to the server start, we'd have to establish not only the "proper" activation conditions, but numerous "contingency" conditions
for both sides, to cover what happens in the event of any ahistorical situations, geared twoard bringing the war back to it's proper "ebb and flow" ASAP.