Of course you should write "-?[0-9]+" when you need it! And for interactive use -- search-and-replace, say -- the conventional notations are not bad, since they are compact to write, you have the meaning all in your head anyway, and nobody is going to look at it later on.
I think the purpose of this thread is to ask for emacs to support PCRE regexpes in commands like `query-replace-regexp`.
Would this even be possible? I can imagine a whole lot of packages breaking if the regexp syntax changed, and changing it just for the user input in interactive functions looks a bit sketchy.