I'm actually planning to put most of my points in the Motion tree. More and longer phase locks, and it bouncing to another target if the first one dies? Yes please. The rest of my skill point plan involves getting Wreck (because that bonus is just ridiculously huge, and with all the Motion stuff it'll be active a lot) and Minds Eye because I like sniper rifles and phase lock makes getting headshots easy. My multiplayer build will also pick up Res because it's such a potential game changer in a team and I'd already qualify, and I'll probably pick up a little Elated too, but I'm not planning to go any further than that in Harmony.
I've tried it out now, and there's no way in hell that the time between novas is 2 seconds. More like 1 second, or even less. And it needing a full recharge before starting again isn't much of a problem because by the time it stops everything's dead. Combat almost degenerates into just running straight at the nearest enemy and watching him die burning, possibly after nicking me a time or two (most likely with ranged attackers) and extending the novas. Of course, I see how many I can take out before that happens, but any time the shield does drop it usually finishes the battle for me.
Flame of the Firehawk is a pretty strong candidate for best shield in the game, I think. Assuming it scales to your level when you get it, I might postpone that quest in playthrough 2 just to get a twinked out max level version of it.
In other news, the last few posts have convinced me that I should search for and try out a Dahl burst fire sniper. I've been using mostly Jakobs snipers so far, but if the bursts don't disrupt accuracy too much the multiplier from extra shots might be worth a drop in damage per shot.