Right now, you can do it in two ways:

• Don’t have the Arch key at all. supac will silently skip it.
• You can write a small wrapper in package.nu that checks the presence of your preferred arch package manager in $env.PATH, if it’s there then it’ll insert the key and value, and not otherwise.

I’d mostly go with 1 unless you’re sharing your non-arch config with an arch config on two separate machines.

Yep, it should cover you alright! I use all the 5 package managers mentioned here (hence the order :p). Scriptability and post hooks in particular make it even better (cloning/copying dots, activating systemd units, other stuff, etc).