Initially the max coins were around 70 billion during the POW phase.  However, due to the nature of POS, the max coins will always be based on the minting reward which keeps the network running.  Currently the minting rate is up to 10% of outstanding coins but will be up to 5% soon.

coolbeans has shown some stats in relation to actual users minting over time which may help answer your question...

https://www.reddit.com/r/MintCoin/comments/4om5kb/mintcoin_financial_and_statistical_analysis/