Bitcoin is decentralized. You will never get 100% of the community to agree on just about anything.
If you want to start using mBTC then us mBTC. Personally I think it is a little early for that. A $1300 ASIC miner would for example be 65,000 mBTC which is a little excessive IMHO but the reference client already supports multiple unit types.
Probably the best thing to do is to start lobbying your favorite webservices (blockchain.info, MtGox, bitmit, etc) to support an option to switch to mBTC. I think common usage will happen organically once if/when Bitcoin trades above a couple hundred dollars. Sorry I mean 1 mBTC = > $0.20 USD or so.