New pilot cards wouldn't be difficult when it came to picking characters from the EU since they have been dipping into it every now and then, although mostly on the imperial side. What would worry me is new pilots mean new abilities and these could be exploited or imbalance the game if they didn't have enough testing, but that said I am not against extra pilots for the new tactics.
Droid and weapon boosters would be nice as a seperate pack although again I am not sure what else they could pick from the weapons that would fit. What could they add for the Imperials? Droids are great for a rebel player but it leaves the imperial player a little out in the cold just because the empire wanted cheaper fighters.
A scenario booklet would be cool but I would wonder how well it would sell since it isn't hard to come up new missions on your own or in a gaming group. I remember they made one for tide of iron and I heard it didn't sell well.
I hope FFG don't drop support for the product after the inevitable B-Wing and TIE bomber. I want new models that go into the EU territory since there are plenty of cool ship designs that would be great for X-Wing. They could do Clone wars era, which seems the most logical but I wonder how many people would want ships of that conflict when the empire VS rebel conflict is far cooler
And what's wrong with adding a Skipray Blastboat, R-41 Starchaser, Z-95 Headhunter, Star Viper, Outrunner/YT-2400, TIE Avenger, TIE Defender and many more? It's better than a repaint of any existing model which you could do yourself anyway and would add new ways to play, new scenarios to create and far more variance to this awesome game.