I've been playing indoor & out at a high level now since 1986. I've got three rule changes that I'm asking folks to kick around.
Without further ado, I'm going to just throw these out there and see what kind of havoc they wreak.
1. (Indoor & outdoor) Remove the over-the-net rule.
In general, players can more easily kill balls that are closer to the net. The logic for this rule proposal here is simple: pulling the passes off the net so as not to be interfered with by blockers will also pull some of the sets (not all) off of the net.
Further, this would get rid of the stupid call refs make when there is an overpass, the ball would clearly be going over the net if left untouched, no one on the passing team is making a legitimate attempt to play the ball, a blocker reaches over, blocks the ball, then gets called for being over the net. That one drives me crazy sometimes.
2. (Indoor & outdoor) Remove the screening rule.
No one calls it. Ever. All anyone does is yell about it. I've seen classic screens that fit all of the criteria (players close together, ball traveling fast & at a low trajectory over screening players, etc) and still don't get called. Save the ink & arguments; remove it from rulebook and let 'em screen. In outdoor doubles, most players are courteous anyway about it, but it hardly even matters. It's easy to see around a single-person screen, anyway.
3. (Indoor only) Add a bonus attack line for a two-point play.
This one would be fun, I think. First, define a kill to be a legal attack hit that causes the opposing team to commit a fault after zero or one opposing team contact. Now, add a rule that says that if the attacker is completely behind the bonus attack line at 6 or 7 m back and kills the ball, two points are awarded to the attacking team. Add verbiage that makes served balls defined to not be attack hits or add an exception that served balls don't count for two-point plays.
What makes this interesting, IMHO, is that if I were coaching to defend against the two point play, I'd tell my blockers to stay down and everybody dig. This would definitely prolong rallies and make things pretty exciting.
My $0.02. Yours?