There are already several pegged well-known cryptos on Steem Engine:

And you are right, all the communities that exist around those cryptocurrencies can start a new token on Steem Engine and empower their community with Tokenbb.

I'm not sure if the pegged token can be used as a reward token (unless they can fill their own reward pool with their native cryptocurrency, maybe.) but nothing is stopping them from creating a separate reward token for their own cryptocurrency through Steem-Engine to reward their own communities.

This token will be tradable for STEEMP on Steem-Engine and from there (through the pegged tokens) to their native chain.

Cool idea! I do think you are on to something. (I need to think about this more.)