SMT does not run on steemit.com, but on the blockchain. You would still build your own frontend where the new coin adds functionality.
That's not compulsory. It's advisable, but not compulsory. We don't know yet how many SMT-powered websites will run on separated websites. The cheaper approach is to start it where you already have a savvy and experienced community, so probably many will be started here, on steemit.com.
I'll dig into this matter a bit more. If you're right then I see no added value at all for SMT 's that use steemit.com as their frontend, unless you're able to also adopt the look-and-feel of steemit.com for your SMT-based app.