Electric armor is great, but I notice a conspicuous lack of fire armor on your list there. Especially given that the three primaries you suggest don't require redraw, you should consider giving it a try. It's a somewhat squishier, much aoe-ier version of electric. Since you plan to do the incarnate thing, and presumably some IOing while you're at it, your squishiness should approach zero as your level approaches 50+3 regardless of your secondary set.
Again, elec is great, but considering what you've already played, fire is probably more different. I personally find its increased clickiness more engaging than elec's set and forget style, as well.
So I've just returned to the game after several months away (in fact in the last couple of years I've probably only played 4 months in total) And I have discovered I no longer want to play anything but scrappers. I have capped Tanks, Trollers, Blasters, Veats, Corruptors, even a defender, but only my scrappers are getting considered for the Incarnate system. However I don't want to burn out on the incarnate system so I decided I will be making a new scrapper. I'm struggling, however, to decide on the sets. I currently have capped:
Spines/Regen
Katana/Willpower
Fire/Shield
Claws/Regen
Broadsword/SR
Spines/Dark
Dark/Regen
i've had various attempts at levelling an invuln alt but they have never seemed to really take off the way I'd hoped. I've played Dual Blades to the 40s and just don't like the concept of it. Got a couple of WP tanks so don't really want any more WP alts. This leaves me with the options to try something new of:
Kinetic Melee
Electric Melee
Martial Arts
The only defense set I haven't played much is Electric Armour, however I wouldn't be averse to trying another shield based alt as long as it was sufficiently different to fire/shd
As far as I can see this leave the following options:
kinetic/Electric
kinetic/shield
electric/electric
ma/electric
ma/shield
(discounting elec/shield due to similarities to fire/shield)
I'm just wondering what peoples views on any of those combos is.
Sorry for the long post and thanks in advance for any feedback