I really like the idea of relief pitchers having to throw to more than one batter (I've suggested it before here). There's nothing worse than seeing innings where you get like 4 pitching changes in a row. Completely kills any kind of momentum in the game. I'd say each pitcher should have to complete 3 full at-bats, or have the inning come to an end. You can make the rule only for the regular season if you really want to. As for the shifts, definitely NOT in favor of that. I'm okay with a pitch clock, as long as it's only designed to speed up a few of the "human rain delay" guys.
I think it would be interesting to experiment with added visibility on the balls, to allow batters to pick up the ball and spin a little easier. Not sure what the results would be, but it could be played with in the AFL, etc.