Hello
Some notes on the patch:
- the subst is being handled at top of paramsubst, because it's made
uncompatible with (...)-flags (${|(U)funct;} looks awful, more on this
in the patch),
- then the `s' variable is advanced past the semicolon, so that the
rest of the function can safely progress doing (almost) nothing
- one thing that the function still does is a fetchvalue, which I
prevent from setting vunset to 1 in case of ${|func;}

If commited, the substitution will be super useful in // substitution. E.g.:

arr=( val1 val2 abc1 abc3 )
func() { REPLY="${(C)match[1]}"; }
print -rl ${arr[@]//(#b)(*)/${|func;}}

Output:
Val1
Val2
Abc1
Abc3

PS. I did install mksh and test the substitution, it works the same.
-- 
Sebastian Gniazdowski
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