TL;DR
I think now with the UI update coming up there's a good opportunity to improve ease of use of the train commands, and with the addition of parentheses you just make everything so much easier and neater.What ?
One way you could implement it is to add a "tab" button which creates a parenthesis by moving the conditions inside the parenthesis slightly to the right, eg a*(b+c)+d would be:a
-b
-or c
or d