Honestly, I think the choice of only having 21M possible BTC was a design flaw. Precisely because its going to force us into an unnatural and unwieldily situation with regards to decimal places. What do you even call .00001? Why introduce this complexity in the first place? In retrospect I think it would've been better to have a 2B maximum cap, solely for the reason is it would help keep notional representations into the whole integer range.
This is a non-issue, make a client that displays your balance in nanoCoins and BOOM, your supply is now 21,000,000,000,000,000 NTC
Protocol and client evolutions will introduce 10 extra decimal places if it ever becomes a need.