I think first layer is a must, and layer 2 can be an add on. Some SMTs will want to be easily upgradable, and for that we will need layer 2.
But other SMTs will never want to upgrade. Not being upgradable has its own advantages. Would you buy Bitcoin if inflation could be changed to 15% a year? What if I want to create an SMT with 0% inflation and keeping it all layer 1 so that everyone knows it will never be changed?
That's why we need SMTs on layer 1, not just token balances but also inflation rate and all the other attributes which steemit devs already coded.