I also added the wee RF 16/2.8 a few weeks ago, giving me a small and surprisingly good UWA for the R6.
This makes my kit the following:
R6
16/2.8, 24/1.8 IS Macro, EF 50/1.8 STM, EF 70-200/2.8 L IS v1, RF 100-400/5.6-8 and an adapted Nikon-mount Tamron 90mm f2.8 AF Macro (plus all my old Nikon MF glass if I decide to pull it out of storage)
I will still like to have a second body, but that will be either adding an R8 for light carry, or demoting the R6 to backup and adding an R5 or R6II to maintain battery commonality. Both options are viable (even together in the long term)
In terms of lenses, the next priorities for me really will be a fast 35mm and either the 85/2 IS Macro or the EF 100/2.8 L IS Macro, so I can go all-in on native or EF lenses for my common work and get a real replacement for the R7/RF24 combo. For the 35, it will probably be either the RF 35/1.8 IS Macro or a used Sigma 35/1.4 Art in EF, not sure which as I'd like both the size of the RF and the speed of the Sigma. Beyond that I'd like to add the RF 14-35/4L and RF 24-105/4L to round out a zoom-based hiking kit. The RF 14.x Extender is also on the to-acquire list. I might add the RF15-30 & RF24-105STM as interim/ultra-light options.
I also finally started to add UHS-II cards to my arsenal, we'll see if I even notice the difference. Not a lot of stuff I do really stresses the buffer on my R6.