On a recent thread (
https://www.bikeforums.net/bicycle-m...ad-triple.html )
under reply #8 there was mention that Shimano's latest 11 spd cassette, the 8000 series Ultegra 11-34 is back compatible with 10 spd hubs
sort of like the 11 spd MTB cassettes being compatible with 10 spd hubs. Researching this gave some incomplete data but may
be worth exploring, as a way to keep your present wheelset (ie some Shimano sites show no 11-34 11spd, others do but no other info).
The 8000 series Ultegra 11 spd RD can go to 11-36 as is and likely to 11-42 with a Wolf extender. There have been a number of posts
about the electric SRAM and Shimano RD being pushed 4 teeth larger on the cassette than their nominal max. No reason this would not
apply to the mechanical RD as well and the 8000 series Ultegra is clearly designed for larger cassettes than the 6800 series.