I'm looking forward to see how this develops.

There was a program a long time ago, classic Mac OS days, and I don't remember the name of it but I think it was "<something> Consistency". I loved it because tasks in it were "loose," in the sense that something like "water the plants" didn't have to happen on a strict 7-day repeating event. It could be defined as "should be done 6-8 days after the last time I did it." So when you hit "done" on the current "water the plants" task, it automatically fuzzy-scheduled the next "water the plants" event with a target date of 6-8 days after when you clicked done. You could have the range prefer some days but be "acceptable" for a wider range of days.

Someone once told me emacs org-mode might be able to schedule recurring tasks somewhat like this. But any time I see a new calendar/to-do manager application, I hope the designers keep this "fuzzy" repeating event idea in mind!

Things 3 has a sort of recurring todo like what you're describing, where you can set like this: https://culturedcode.com/things/support/articles/2803564/

Maybe Sciral Consistency?