I think, in recent years, invasions have used allies as a way to almost prop up their numbers on their side. I think invasions should be largely, if not fully, faction-specific or faction-centric stories. The characters and stories involved should be in that faction. Now I would like a limit of ally slots, but I, and I imagine some other people, am concerned with people willy-nilly joining major factions just prior to invasions. That's a lot of self-policing for faction owners to do.
I think also what this does is not necessarily force, but encourage other roleplay like annihilations, junctions, skirmishes, etc etc. There's nothing saying that a skirmish can't be a big-ass affair with IC consequences.
So my question is, hypothetically, allies go away- (I'm not against it). What's the rectifying action for people joining major factions solely to participate in the invasion? Is there going to be that at all? Because, we have, for example, Imperials not aligned with the GE signing up for the GA invasion. Makes sense in-character for them to oppose another Imperial faction whom they're at odds with. But it wouldn't make sense for them to be in the GA faction necessarily. So is there going to be a limit on people joining Major Factions, or factoring that into account if someone joins a Major Faction days, hours prior to the invasion?