I don't work for Pioneer but I can tell you that you can not "control" Rekordbox from the RX - Rekordbox is not midi mapable.
You can connect to it via Pro-Link with an Ethernet cable - It essential uses your mac/PC as hard drive. you can drag & drop files to the player.
* *Tip - You can map keyboard short cuts for loading tracks to either decks of the RX this helps speed things up when your at a gig using pro-link. I mapped alt/option + Left key for deck 1 and alt/option Right key for deck 2. Its a lot nicer this way as I find that sometimes when your trying to drag a song to the link player section at the bottom of the screen sometimes Rekordbox assumes your trying to move the track to a new playlist etc. so as your dragging the track it starts scrolling your list. using a keyboard short cut totally eliminates that issue!!.
- Personally I agree with you that being able to scroll around with Rekordbox via the scroll wheel on the RX would be amazing but like I said currently Rekordbox is not midi mapable.

