I have an idea about how to think about the 2 target rupture cleave scenario but I haven't had time to experiment with it.
A couple weeks ago I did a little test in ShadowCraft to motivate the analysis but never got around to doing the analysis. I hacked ShadowCraft to handle two different situations, first a situation where your rupture is being applied to 2 targets with no loss in envenom uptime, basically I magiced combo points out of midair to see what would happen, then I did the same thing but this time counting those rupture cps against the cp resource pool leading to less envenom and less envenom uptime.
2x Rupture Magic CPs, DPS: 455191:
2x Rupture Real CPs, DPS: 422238
This basically follows expectations, in our magic CP case the value of haste declines substantially because of the substantially increased energy regen and it is somewhat stronger in the real CP case but energy regen is still higher than before. Mastery substantially increases in value from the additional VW and dp ticks and crit loses some value from the additional energy regen although it does lose less value because of the crit is less dependent on energy regen.
TAKEAWAY: The reason I didn't want to share this simple test is simply that its incomplete, it assumes that the player somehow keeps a 5 pt rupture and full dp uptime on 2 targets. This is somewhat unrealistic and likely biases the results somewhat, I suspect toward mastery because lower cp ruptures have lower energy efficiency but I'm not certain. There is a lot more to be done here but the basic results do appear to confirm that mastery increases in value haste decreases in value and crit remains relatively stable in a two target rupture multidotting scenario however this analysis probably isn't precise enough to quantify the magnitude of the effects.