There would definitely be issues with the keyring being outdated which you have to know/search how to work around. And from time to time Arch also requires some

There would definitely be issues with the keyring being outdated which you have to know/search how to work around. And from time to time Arch also requires some manual interventions in the package update process (that are posted on archlinux.org) – you'd have to deal with those all at once if Arch wouldn't have been updated for a very long time. But, other than that, I can't think of other reasons why having a less often used Arch installation would give you trouble. Then again, I haven't used Arch in such a manner, so you might as well be right.