Sure. If capturing is supported for this formula, I would like, rather expect that we could invoke the variable nomenclature of $1 to refer to it. It does not appear to be supported.
Since the substitution or replace input is a string and you have to escape certain characters I tried "\\n" to create a newline - no luck; tried to refer to the capture variable - $1 - highlights as yellow - not supported
RegexReplace( [Notes text], "([.!?])\\s*", $1&"\\n")
Looks like this might be an enhancement request.
*edit: for some reason the solution isn't showing in the thread; posting here. Access captured data with \1, which has to be escaped.
RegexReplace( [Notes text], "([.!?])\\s*", "\\1\n")