I do think, like it or not, the DH is here to stay. Partly because before this year, every other level of baseball outside the NL had it. This season gave the perfect excuse to implement it. I saw Snitker gave the DH his endorsement, and I suspect more managers and other NL people will do the same.
The extra inning rule does not return, I hope. Just too much of a gimmick to me.
The three batter rule I think, is here to stay.
The wild card round was needed this year because of the 60 game schedule. Assuming we're back to 162 games, I don't see a need for that round. I don't see another change needed for the postseason format until MLB expands to 32 teams, which I believe will happen in the next 3-5 years.