Thinking about it, still has quite a bit of work involved, mind. and will still need to be around the time signature. OK-ish for simple basic ones( 2/4,4/4, etc) quite more complicated to complex ones. Maybe best way is design an embeded metronome with a led, to solve the time issue.
as quantizing goes, you have to think about the division of the tempo, and you know how auto quantizing is prone to mistakes(live aint a good thing), So id probably just stick with the arpegiator side of it. what synth you have?!? Most can do quantizing themselves
Wouldnt it be much easier to define the tempo on the synth, and maybe have the arduino read the MTC ?!?! http://www.sparkfun.com/products/9595
maybe you can start with this for your tests and exxperiment/dev of the code, etc