How many high-end audiophile headphones are actually wireless? ... And how many wireless headphones also provide a wired port?

I'd say wired is going to be around for a while yet.

Ultimately its up to consumers to tell companies what they want through their purchases. Regardless, even if it turns into a market niche, as long as there is a profit to be made, companies will continue to provide the goods.

Remember the the introduction of the CD? Many said vinyl records would disappear within a few years but look at them now...

Now on the topic of convenience, even if you only own bluetooth sources you can continue to use a portable dac/amp with bluetooth capabilities along with your wired audiophile headsets...

Edit: clarity