According to this many/most experimental features already produce warnings.

But I have to say that I wonder what you would do with the information produced by such a flag.

• If this is your own module; you presumably thought about the implications when you chose to use the construct.

  Are you going to change your mind and remove it?

• If this is someone else's module:

  would you refuse to use it because they've chosen to use an experimental feature?

There are several experimental features I've simply refused to use because it was too confusing to understand their syntax rules; or too unreliable in use: eg. smartmatch.

But if I found a module that did something I needed to do; but noticed it used smartmatching to do it; that wouldn't stop me using it provided it appeared to work correctly.