I really don't see LF cameras as being any way in danger of disappearing, and the same people making the cameras will almost certainly also make holders. The plastic holders in circulation now will last as long as any plastic thing. Whether or not any of it will be 'cheap' remains to be seen, but photography has always been an expensive undertaking. Cell phone jpegs shot to email screens is probably as affordable as photography's ever been. Paradoxically, I think it's making the whole film experience (at least LF) all the more attractive.