The Nexus 7 updated first thing after booting on day one to 4.1.1. Seems pretty tight to me. I sang a few bars into track one, replayed and sang along on a second track, which seemed to sync fine, using the internal mic. No time right now to do measurements on the oscilloscope for meaningful tests, it's moving day tomorrow and Saturday. The android app is marked down right now at €3.99 or $5.10 is what I paid, normally €5.99 for the Android app. I think the multi tracking will only work well with hi-end devices and the 4.1, as you wrote!
I had not heard about the audio latency improvements with 4.1, but I can tell you that I am extremely happy with the Nexus 7 (16gb), very fast and elegant. The instrumnt apps are all showing improved performance with very acceptable latency now. Leon is a theramin app that kicks on this thing. Plus you get $25 at Google Play with the Nexus 7, so Audio Evolution, Leon and a few other cool apps were basically free.