Back in the day, the way you put in a feature request for X-Plane was to email Austin - his email address was all over the web site. So was his phone number - if you really wanted the request you could just call him, but it might hurt your chances. Austin had a big text file where he copied all of the emails, and then he randomly jammed things into X-Plane. It was the wild west.
Fast forward twenty years - we have a development team, we have customer support, we have an art team, and X-Plane has a lot more users than it used to. So we made an official place to record feature requests: feedback.x-plane.com.
The feedback request board allows for voting, so please look through the existing requests and up-vote it if it's already there-this lets us easily find very popular requests.
The request board covers X-Plane desktop and mobile. You can also request features for end users ("better clouds") or for third party developers ("scenery packs can edit the mesh around airports"); it's all good.
Looking through the "most wanted" right now, it looks like our internal high priority items (most of which are in progress) match the most wanted list pretty well, which I think is a good sign for our upcoming dev work.