This is something you can kind-of do in chia lisp, you just have to do it manually if you want to. The standard transaction format implements the base taproot idea of being able to switch from providing just a signature to involving some more complicated script, calling it a “hidden puzzle”. To do that, it generates a hash of the hidden script via the custom sha256tree1 function. I don’t think it would be much more hassle to add taproot-style MAST (where you just have a top level merkle tree of scripts, choosing one to evaluate), though you’d need some cleverness to resolved a deeper AST (replacing (i COND CODE hash) with (a (i COND (q . CODE) (q x))) at the same time as building up the overall hash of the expression, perhaps).