So we should just assume that any future technology we would like to imagine is assured of happening, given enough time?
If that is the case then I don't need to waste my time with cryonics because I am assured I will be resurrected in a Tipler Omega Point.
The argument is not that everything that seems possible is inevitable. Rather it is that this particular area of possibility-space is a generally reasonable one given a reasonably allowable timeframe for cryonics patients to be stored. Current advances in printing organs, scanning connectomes, building nanomachinery, etc. are pretty good indirect evidence of that -- provided the loss of structure isn't excessive.
Luke Parrish points me to what is clearly by far the most serious critique of cryonics ever written: a 57-page treatment by Evelina Martinenaite and Juliette Tavenier, presented as a 3rd semester project at Roskilde University in Denmark supervised by Ole Andersen.
Full paper