Communities as you see it (Github) is not just "good enough" it's too complex / a disaster in the making.
I don't think it's asking for much to add "Top of the" day / week / month / year / all time. This is what Reddit has been doing and that's how people consume niche content.
Your definition of communities should be just that at first "Niche content" before you start handing out moderator access to keywords.
Do the same thing as Busy.org does, Allow people to select a bunch of their favorite tags to the top of the UI
Then either generate some condensate of liked tags or allow for full boolean selection of tags.
Top of "TIME_FRAME", Favorite Tags on top and Splits the posts and the resteemed are mostly UI jobs and should take less than a day of work.
My two cents
just good enough
Communities : (See above) Effortless Onboarding : Will never me good enough. A Mobile App : eSteem is more than good enough.