I have them hooked up on my DVD recorder along with my VCR and those play fine on my HDTV.
I think tube TVs should be able to get their backlights, guns, whatever makes them tick, replaced not too easily but not too difficultly.
I think new backlights, guns and that could be sort-of easily made, and thus tube TVs could be revivable if that's the case.
you could always get composite cables for the systems. I played some of my ancient systems on my friends new hdtv through composite. I have one of the last generation tube televisions and I got it on purpose because I hate playing old games on flat screen. It doesn't look right