You have a fantastic export tilemap option! I am sure it will save me hrs of time developing my little 2d platformer.
It sends out to JSON which is great as I wrote a tool for that to import into Unity3d.
However, It would be great to have a import tilemap option as well. This for a couple reasons. I may make changes in Unity I'd like to see in Pyxel. I also use an IOS sprite app called Sprite Something which is great on the go but is less featured than Pyxel that I would like to import it's tilemap as a JSON into Pyxel.