This is a very interesting question.  In Vegas, someone took the time to explain that 'Bitcoin' was the network and protocols and community of participants - while 'bitcoin' was a unit of account.  That is, 'bitcoin/Bitcoin' are actually two different things.  

Now we are faced with the notion of 'millibitcoin'.  Those who are not computer nerds hate things like 'milli', 'micro', 'nano'.  While scientific notation makes most of us squirm and giggle in our seats with great joy, it is a pain in the ass to real people.  

Mastercoin is the protocol and community as far as I am concerned.  I'd even be delighted if we had no currency.  Let bitcoin be the currency.  It is a good currency.  We don't need another one.  But we do have to name the unit of account of Mastercoin.  Mastercoin is a very dumb name.  That is the name of the system.  Lets give the unit of account for the Mastercoin system a distinct name.  

Bitcoin will forever fuss about with millis and mBits, and so forth.  It is a serious impediment for the simpletons to understand.  Without a good nickname, the unit of account is hard to understand.