So what are my odds of swapping a 3070 ti with a Radeon 6900 xt without reinstalling? Theoretically it should be fine, uninstall nvidia-dkms install amdgpu packages. Reality often doesn’t match theory, however.
I’m fine for reinstall, but time saving wouldn’t hurt either. Any thoughts on specifics I need to do?
This shouldn’t be necessary.
While using your old novidea card, uninstall all novidea stuff, delete all configs related to novidea, shut down your computer, unplug it from power, disconnect the monitor(s).
Swap the cards, reconnect everything. Turn it back on. Hopefully, everything will work fine.
If it doesn’t boot, there is some step I forgot 
Have a USB stick with an EndeavourOS live image ready, just in case. Not to reinstall, but to use a web browser in it to come here and ask for further help, and/or chroot and install any missing packages. Though, I see no reason why you wouldn’t at least be able to boot to TTY.
Should be able to remove all nvidia related packages shut down and remove the card. Install the new card and boot up on the new card. It will boot on the amdgpu kernel module. Hopefully there are no issues but be prepared just in case. So save whatever you need to in case a reinstall is necessary.
Edit: As @Kresimir said make sure you have power disconnected and you ground yourself while handling any of the components you remove and install while inside & outside the case. The 6900 XT is too expensive of a card to have it damaged installing it.
Thanks all. Arrives tomorrow so I’ll get 'er done.
@ricklinux It’s been a while since my building days (yay SATA came out!) I thought these new cards were hot swappable?
It only takes a static shock which equals 10,000 volts and it will be swapable from the slot to recycle bin!
Card didn’t get here until this afternoon but all tidied up and working great. Just FYI, could not get my monitors to display properly until I did in-fact install drivers.
Prior to that I did an xorg -configure just to see what it was pulling and it couldn’t find anything but a generic device.
Following Arch Wiki for AMDGPU I installed:
xf86-video-amdgpu vulkan-radeon libva-mesa-driver mesa-vdpau
Following that I noticed the display output names changed and my WM was happily working on all monitors again.