No, that would be boring. Too much temptation for people with grudges to time their entry into the war until the CE/Tara block was too crippled to recover, but not too long to put a stop to it before all is lost.
What would be *interesting* is if the invaders started picking off the small guys individually. Then you'd really see some scrambling. Would the northern realms pull it together fast enough, and drop their internal conflict in time to stop it? Would the CE/Tara block abandon their grudges and save them, or let them die and count on their power/unity to defeat the invaders on their own?
That would not be fair either. CE would just blackmail the northern realms: "I'll save you if you do this, this, and this..."
Please leave any experimental projects like "IR-free island", "no character limit island", etc., to Beluaterra, because:
1. Other islands are exposed to new players, whose first impression of BM will be whatever island they started out at. Beluaterra is populated with players who have at least experienced a little bit of the other islands, because they had to have immigrated to Beluaterra. Imagine a new player who started out on an IR-free island, plays for a year, and then immigrates to another island, and gets a military leadership position. Guess what he's going to do? What if he's used to stuffing five characters in one realm? Will he be tempted to multi-cheat?
2. Players in Beluaterra signed up for crazy stuff happening. Players in AT and EC just want a "vanilla", basic BM experience. Is that so wrong? As someone mentioned earlier, some of us play BM for new thrills, and some of us play BM for familiar comforts.
Finally, player retention is a problem, yes. But if we invite in clanners? Then we'd have two problems.