Acid Blade is the best trick Concealment Ops have, awesome synergy with Tactical Opportunity skill, deals INTERNAL damage, gives armor penetration buff, all of that in off GCD ability. I'm perfectly fine with it as it is (after 2.0). If it would be passive - yeah, things will be certainly easier, but I think you will stop noticing it at all, stop appreciating what it does
Reducing energy cost is always welcome, however it wouldn't do enough in case of our energy management. Personally in addition to Culling I like the idea of buff to energy regen (for example increased by 50% for 2 seconds) every time you use Laceration, if your energy is below certain level, let's say 30%. This could help us back to our optimal energy level, when we had to overextend or we didn't have luck to Collateral Strike/Culling proc (It's surprising how often it happens to me, out of 3 Lacerations in a row none triggered Collateral). Duration of buff, regen value, border energy level (and maybe some internal CD) should be changed, tweaked to adequate level but I'll leave it to more math oriented minds
In fact of leaving combat. Yes it's strange, sometimes it takes - literally - minutes, because the guy you hit over a dozen seconds ago (with not a DoT), still fights somewhere there. It would be nice thing - leaving combat takes 6-7 seconds from last activity (dealing damage or healing other people in combat, taking damage that isn't a DoT), so you can restealth after a Flash Grenade (assuming toned down Medicine Ops). It fits to definition of slippery, I guess.