Hopefully the expansion and crew skill cap increase will not make all prior materials totally worthless, but it would not surprise me if it did. That being said, RotHC is NOT of the size and impact of a typical MMO expansion. Furthermore, BioWare has done a decent job of keeping old gear relevant while continuing to add new gear as the end-game content has grown. I do not see RotHC being a total "gear reset" like other MMO expansions sometimes are.
So, there will be a market for molecular stabilizer crafted gear, but the demand will decrease as it should.
Level 50 FPs give black hole gear and iirc, ev/kp nim will give dread guard/hazmat, so one would think they will be worth something but without knowing what kind of drops you get from Makeb while questing, hard to say.
Though it definetely sounds like campaign/dread guard will be leveling gear for 50-55. Probably a heroic 2 on makeb will drop hazmat, lmao