Input lag isn't inherent to Android-- there are plenty of other emulators working fine on the oDroid C2 under Android with no issues. The biggest problems come down to two things last I knew---
1. Getting the compilation kit to actually *install and work correctly* is a bitch and three quarters.
2. MG was looking into input handling and several other areas related to Android, but hit some serious snags with our input code as it is that I seem to recall was going to require some substantial reworking.
In the end, it boils down to it being a somewhat hostile build process and no platform champion to push development on that front at the moment as much as we'd like it. If an Android dev stepped forward and said "Hey, I'd like to help out" I don't think anyone would complain about an official push.
Try checking the MAME manual at http://docs.mamedev.org