Think they should fly not only on Soyuz but also on Shenzhou after it's got more flights under its belt. Then it would be triple-redundant, and would bring China into ISS rather than continuing their separate space station.
Shenzhou is larger, more advanced in some ways, capable of docking with ISS, inexpensive, and has so far been reliable. Shenzhou can last as a lifeboat at least as long as Soyuz, and has an orbital module that could be left behind on ISS under its own power for a while after the descent module separates, allowing for certain experiments to be contained there. It could even be detached, go some distance from ISS while some risky experiment is run, and then re-dock with ISS, at much less expense than using a Progress for the same purpose. It would make a nifty addition.
I generally don't like China and that sentiment seems echoed by most in the West and also Russia, Japan, and pretty much anywhere else, but if Earth is going to explore space, best to do it together, with resources combined. Earth has 2 manned launch systems and will soon have 4 -- use them together, then no-one gets stranded when one of them has a glitch.
Think they should fly not only on Soyuz but also on Shenzhou after it's got more flights under its belt.
That is a necessary but not sufficient condition. An additional condition is that China *must* open up their program to outside insight to at least the extent that ESA and JAXA opened up their ATV and HTV programs to Russian and US insight.
China has shown no inclination so far to do so.