Blackstone fortress tile system is hex based rather than squares. This throws off the movement system in space hulk, it also changes how close combat and flanking works. I wouldn't mind getting my hands on a box of blackstone fortress, lots of nice models and the AI mechanics are great.
The other problem is blackstone fortress is small, 4 player models, with a 5th player being the enemy. I'm running a campaign for 6+ people, so needs space for 12 or so player models place a horde of bugs
I think worldworksgames is probably my best bet, they have options for 1.5 inch squares which will help with GW's ever growing base sizes. There are some amazing 3D stuff around as well, which would be awesome but it aint cheap.