I weigh 165 and a front wheel spoke broke last month on my C24 9000 tubeless wheels while visiting in Tucson. That made the wheel unrideable. No one in town had the proprietary spoke. The rear wheel has two different proprietary spokes and the front wheel has a proprietary nut used at the hub. I now have a spare of all 3 spokes and the nuts are on order and were not easy to find. What a pain. I will probably not buy wheels with proprietary spokes again.
I've got a pair of the ultegra tubeless, and I've had front and rear spokes snap.
The rear would turn okay despite being taco'ed, but when the front went, I ended up doing 25 miles with it rubbing on my fork leg every revolution. Good job it was only my winter bike!!
Whilst they feel good as a wheel, my take is that:
a- the rims are made from putty, they are that soft. 1 uk winter of fairly light riding has killed them.
b- if you are looking at tubeless as an option, then the need to use shimano's own valves (without a removable core) makes getting the job of seating the tyre a complete pain. You just cannot dump enough air in quickly.
c- the hubs aren't up to the level as the true groupset hubs regarding sealing etc.
Might be worth looking at Bontragers paradigm wheelsets- hits the wide rim mark, good hubs, lightish, good reputation regarding longeivity, (spokes not normally right at their elastic limit etc ime), and all backed up with a good dealer network if needed.