So I know that we have the ability to define multiple client groups and change the adlists/blocklists/whitelists for each one. I also know that clients are assigned to "Default" automatically unless you configure them for a different group. New lists (ad/block/white) are also assigned to the default group unless you change it.
I propose a feature whereby you may select an arbitrary default group, not only for new clients but also for new lists. The ability to choose the default client group is not strictly necessary, but would not be difficult to query the list of groups and present a choice (and probably display something like "(client default)" next to its name in the group management pane.
My default group has very minimal blocking. Basically just stevenblack + some broad whitelists since my visiting family members would complain about Google search ads etc being broken. Rather than remembering to configure each guest device that joins the network, I just made the default group as non-breaking as possible. This means my most used devices are on another group though, so anytime I need to allow/block a domain on my device, it takes an extra step to go assign the group correctly.
If I could instead configure it such that changes to exact/regex blocklists and whitelists apply to certain groups by default, it would remove a step. It would also make many external tools for adding domains work properly since most (all?) just add to the default group.