I think they'll both do well. it depends on the use case.
I think tribes favors organized businesses where as SMTs are basically for anyone just screwin' around.
With a tribe you have your own domain and control of the website. For most SMTs you'll just be using steemit.com. So, if you manage a millenial trans furry history group then SMTs are the spot you'll want to be. If you're managing a brand I think Tribes make more sense. All that said i still imagine people will get both. Some ease of use for posting as an SMT and ease of use for trading as a SE token.
Steem-Engine smart contracts will continue to have a lot of use! I trust your team has all sorts of ideas up your sleeves, like the recently released NFT's!
STEEM can support so much great activity, that customjson layer is great, fast, free.... I wouldn't be surprised if we see even more STEEM sub-protocols by the 2022 date you mention.
For 2020 I am building '#STEEM-as-a-service' - keep building!