These things have been going on OFF and ON for as long as I have been on steemit (about 13 months).
Some of them stick around, some of them die off. Some of them help for awhile then no longer seem to be as useful. Some of them start out good and then end up being a cash cow for the creators while not really helping the people that much.
It is kind of like life. I can't really tell you which ones to support. I also don't think there will really be a cap. Right now Steemit is artificially being slowed intentionally for adoption. Steemit Inc. has not advertised and they have not opened it wide for joining. In other words, the floodgates have not yet been opened. I expect big things to happen.
It is way too early to predict what any of those will be. There will be cycles though of ideas people already tried being tried by someone that doesn't know about previous attempts. This is again life. There will also be new things mixed in with the repeating cycles.
when you say slowing adoption are you talking just because they haven't advertised?