Hah! This is fun. Reminds me of the excitement of TUE back in the Halo 2 days. Pioneering that was a lot of fun, same with LASO. I love community-orientated projects like this.
I'd love to help out with theories and ideas with the BOBs. My Xbox RRoD's a few weeks ago, so I can't help directly.
What I will say is that I think that this sort of thing would require a straight run through on Solo Legendary, killing one BOB per level, which would be tough seeing as there are spawning issues, but I definitely think that it needs to be a straight run-through to do it. I don't think that the hidden switches have anything to do with it, but if you want to hit them all, I'd say it couldn't hurt to try.
This is actually much better than my old TUE ("The Ultimate Egg") idea from Halo 2, because there's an obvious goal here, which I think is supremely plausible.
My other thoughts are thus:
The mappacks came with updates of sort, didn't they? They added achievements anyway, so I don't see why they couldn't have perhaps fixed some spawning issues with the BOBs. I haven't actually downloaded any of the maps yet (money is tight, yo), so I couldn't tell if there's a difference, and I also can't confirm if anyone else can say if there's a definite link between the Defiant map pack and the BOBs, but what Frankie said in that interview interests me.
"Not built into the...well, people should play it, put it that way". Seems to hint to me that perhaps the helmet is accessible if you have the map pack. But since it's not "built into" it, perhaps it does involve the BOBs.
Random ramblings, I'm sorry. Just thinking aloud here.
I'm not keen on the fake BOBs, but what I do think is that their armour is randomized; it doesn't matter what it's actually wearing, but the point is to kill it. It's interesting that their armour changes and is white, but I don't think it's necessarily something that matters.
So yeah, direct playthrough of the game on Legendary (perhaps not LASO, because god-dayum that would be hard).
Man, I wish I could actually try this myself. Stupid red ring of death.
Good luck to anyone attempting it. I look forward to hearing about this more. I'll try asking around people who may be in the know, see if I can rangle some insight into it.