Kiri Oler at FanGraphs proposes an innings tax to reduce pitcher velocity:

My proposal also incorporates a roster limit on pitchers, but extends the theory behind it in a more targeted manner to protect pitchers with the previously alluded to use tax.

Say every pitcher, regardless of role, starts the season with an allotment of 180 innings (roughly the median IP for qualified starters over the last three seasons), but the 180-inning cap only kicks in if a pitcher throws more than 15 pitches over 95 mph. Meaning pitchers who pride themselves on eating innings can still aim for 200, if they are willing to keep their velo in the mid to lower 90s. Once a pitcher logs 15 pitches harder than 95 mph, the 180-inning cap goes into effect (including innings already thrown on the season). The first 15 pitches act as a buffer, a few freebies doled out to every pitcher so there’s some room for error before any innings tax is imposed. From that point forward, for every three pitches thrown over 95 mph, the pitcher loses an inning from the initial allotment of 180. Under this rule a pitcher who makes 30ish starts can deploy three heaters that top 95 mph per outing and still throw 155 innings while averaging five-plus innings per start. Meanwhile, relievers who don’t need to worry about throwing at least 150 innings, can reach back for their high octane stuff four to six times per inning as leverage dictates, and still carry a workload of 60 to 80 innings.

FanGraphs.com

I like this idea, as I like solutions that provide an incentive without forcing anyone to change. I thought speeding up pitchers could be done with bonuses to those who worked quickly, allowing high earning veterans to keep their pace.

I would add that any reduction in pitch velocity should come with batters required to swing heavier bats, so the game doesn’t get too out of whack.