[Update: Looks like 1UP was off by just about 100 emm bees ... alright, exactly 100 emm bees. The official XBLA file size limit has been raised to 150MB, not 250MB.]
It seems that the upcoming Castlevania: Symphony of the Night will no longer be the exception to the rule -- 1UP's Luke Smith reports that the Xbox Live Arcade file size limit has been bumped up from 50MB to 250MB. The move should allow less agile developers to slip beneath the Limbo pole without winding up in a painfully awkward position. Just ask last year's Lumines Live! how chopping a game into 50MB chunks can make microtransactions even harder to swallow.
Luke also notes that with Microsoft's approval, certain games might even span 450MB. Returning to the earlier Limbo analogy, this would likely be reserved for developers that insist on wearing full suits of armor to the party. The relaxed rules may lead to games becoming more bloated, but the developer is surely better off worrying less about compression and more about, you know, making a good game.
It's worth nothing that owners of the Core Xbox 360 are adversely affected by this decision, as they still find themselves restricted by measly 64MB memory cards (remember those quaint little things?). Microsoft is likely already working on larger memory cards, though even the rumored 256MB variant won't be able to hold many games, much less a 450MB title.