I had a similar idea a while back (can't find the post though), I might dig it out tomorrow. The premise was that a ghost had some sort of glitch in it's programming which still treated the Eliksni as a race of the Light and so it searched out and eventually found an Eliksni who could be revived as a Guardian. Naturally this Eliksni happened to be a Dreg. The standard start storyline is little different than that of any other race of Guardian, maybe with a slightly different first introduction to the Tower. As you progress through your overarching class quest you deal with various Tower and Reef vendors - your "Vanguard" equivalent being Variks - who ends your quest by granting you your 3rd and 4th arms. I think an excellent super for a fallen would be "Ether Overcharge" where you GROW to Riksis size and hit 300% health... While Overcharged you can use all your weapons as normal and gain instant melee recharge but with a slowed "stomp" melee animation that has the same reach as a warlock melee but in a circle. So you have a choice of using the health boost and your normal weapons and staying big for longer (but a bigger target) or burning through your ether faster with repeated melees. Deploying the super in an area that has ceilings too low for you to stand kills you instantly. Movement speed is slowed while big.