I can't say about the extension of realms' frontiers to deserts... but my humble opinion based on no data but the way the devs comment this, I would't expect it to happen.About the trade road, glad you will adapt it. This is the most important part for me.
About the deserts I'm not sure. I like playing with the deserts since it forces you to adapt your expansion taking them into account. the downside is that they don't make a beautiful map.
Before voting, do we know if PDX will implement the extension of the realm's frontiers to the deserts if most of the surrounding provinces are controlled as in EU4?
As for the deserts - I do agree with you. They were added for several reasons and if they are to be removed or not added, some kind of barrier might still be useful there and I would certainly consider it