I thought executed regexs are experimental

/e doesn't produce an executed regex! Instead, it tells perl that the substitution part is to be parsed and treated and executed as perl code. Furthermore, there's no eval taking place, the code is parsed and compiled at compile time.

Note: LSH = regex, RHS = substite

All those features that ikegami lists as experimental, are to be used in the regex part. But /e isn't.