If the rows eventually become static, there are some huge pitfalls with individual FileGroups having mounds of wasted space.... and individual FileGroups by month is definitely the way to go for maintenance especially where backups and piece-meal restores are concerned.

I've solved those pitfalls but it's not easy because of the problems associated with extra space generated during index rebuilds and the fact that DBCC SHRINKFILE hammers indexes for fragmentation.