I'm not sure how KM is going to perform in PvP for non-stalkers. Power Siphon isn't going to get you much compared to build up, unless you're beating up on a mastermind in bodyguard mode, since people move around too much for you to get allot of consecutive attacks off.
That being said, the scrapper PvP numbers for kinetic melee look absolutely disgusting, probably adjusted upwards because of the aforementioned difficulty of using power siphon. Then the only problem becomes that power siphon's to hit buff is only 7.5 instead of 20 like build up, making it harder to bypass defense based opponents.
As far as pairing it with a good secondary for PvP? You can't go wrong with regen, and I've always thought that electric would make a good contender as well. For PvE, it lacks the AoE that elec melee has for farming, but it would be pretty disgusting to see a fully saturated AaO + power siphon shield charge.
So im curious to know, as a scrapper what would be best for the new powerset? I was thinking KM/regen for pvp and KM/Shield for pve or farming maybe? But does it have the potential to be a farmer? Can anyone throw their 2 cents in here? please