I think it actually obscures the important facts about the expression by breaking up the structure which is displayed by the usual infix notation

1. It is a linear combination of a and b: there are two symmetric terms, a scaled copy of a and a scaled copy of b

2. The factors are functions of t alone which goes between 0 and 1 as t does

This isn't litigating about brackets, the traditional prefix notation also displays this structure (though less well than the infix notation IMO)

  (+ (* a (- 1 t))
     (* b t))

I was really only interested in the similarity between the threaded form and the proposal with all the commas (since they mentioned LISP) but I wish I'd had an aneurysm and died before sending the comment tbh.

Yeah, sorry, didn't mean to pile on. I guess my thoughts re the OP are that the common notation for addition and multiplication is not just "what you're used to", but is connected to objective mathematical properties (associativity, commutativity, distributivity).

No need to apologise, sorry for the unwarranted grumpy replies. Clearly it's tough to design for a wide audience, some of whom want to reason about programs as a series of steps, and some of whom deal with compositions of abstractions which may have deeper meanings outside the computer.