I wish to upgrade my bike with the "SRAM Force eTap AXS 2x12 Upgrade Set"; this set would include the derailleurs and levers. The thing is, my current Shimano Ultegra 11-speed crankset (FC-6800) has a left-sided power meter that I would very much like to keep.
What are my options? Will this crankset work with my new 12-speed setup and a 12-speed chain?
Also, can I keep my Shimano Ultegra rim brakes?
SRAM road 12sp is interesting because they claim to have redesigned the chain with larger rollers than the chains most people are used to. For this reason it is entirely possible that the Ultegra chainset you currently have will work very poorly and lead to some damage. On other 12sp systems, it may work or it may shift less than perfectly but a normal (non-AXS) 12sp chain would run on it.
Regarding brakes, these will work. There are considered to be two types of road brake actuation -- Campagnolo/SRAM and Shimano. The reality is that you can use the Shimano brakes and they will stop you just fine and feel OK -- but at the lever the system won't feel exactly like SRAM intended. Groupsets are pretty tightly integrated nowadays -- it seems to be getting more so than less so. It does make changing over from one group to another much less easy than previous generations.
Just to update this for future viewers. Rotor makes AXS compatible chainrings for their chainsets, which happen to fit some Shimano 11 speed chainsets, for example my 105 r7000 chainset with left-handed power meter. It works perfectly and no perceivable issues even when pushing upwards of 1200 watts.
The SRAM 12-speed chain is narrower and is not compatible with the 11-speed rings on Ultegra, it won't be taken up by the teeth. Swapping the chainrings for SRAM rings is not possible either because of the shape of the rings. and the BCD for Sram is 107mm while it's 110mm for Shimano. You could try to resell the powermeter crankset.
Even if you could keep the callipers, of which I'm not sure, I'm afraid you'd need a new crankset as well.
