Is there a way to calculate the potential profitability of a Strat MN?
They will get a 1% fee on the tumbled coins, so if you tumble 100 BTC a day you will get 1 BTC a day.
How is this accomplish on using strats?
What is tumble?
Never heard of doing this before.
Is it like what byteball is doing with bitcoin?

You need 250k stratis to register a masternode. After tumblebit for BTC is ready they will start converting it for STRAT as well.
Not sure about the exact workings of tumblebit, but it acts like a middleman. So if you want to send BTC to me, you send it to the masternode, which then sends it to me. Because the masternode recives bitcoin from a lot of people, there is no way to track who sent me the bitcoin.