Like the idea of flying substitutions, especially when there is a 4th official. Not sure it would work though as teams would just wait for their restart and point to the player dawdling off before restarting. Great idea in theory, in practise, won't change the existing issue of subs interrupting and being used to delay/waste time or slow game down.
Kick ins form ball out of play over the touchline - again not the worst idea. Would be easier to manage restart location. But feels like too much of an advantage could be gained from ball simply leaving the field of play.
Advantages and disadvantages of stop clock been discussed many a time. Sin bins unlikely to happen at top levels.
Self pass for free kicks would be an interesting theory to trial. But would that take spectacular free kicks out of the game?
One thing I sense is that "football" not entirely happy with the rule set at present.