As I understood that there is no inflation on this coin, fixed number of coins is 100 million. What's the point of keeping the masternode?
There is a 1% inflation.
Also masternodes get 1% fee from the tumblebit transactions including BTC transactions. The fee is paid by the users and will reward the node operator without causing inflation.
Exactly, this is not for Stratis, but there is also a Breeze wallet for Stratis, but I don't know is this wallet inflating the annual rate of 1%? I think Stratis users seldom use it because Breeze wallet is the most useful for Bitcoiners.
Stratis users might want privacy as well. I dont know if you will be able to stake your masternode wallet, but from what we know I think it will be possible.
Fees and inflation are two very different things, but my guess would be that the fee for tumbling stratis would also be 1%