Maybe a bit of both. To me, I don't see how a Scout light, once you change the body and the tail cap, is still a "Scout style light" at all. The only part you still have is the LED head. So I do take issue with that terminology.
As for the methodology, I must admit that I had forgotten about the pic rail option. Every single picture I have seen and every discussion regarding the AVA mount seems to be focused on mounting a light in the clamp. Although, if I did mount it using an MLOK rail, I suppose I could just leave the clamp off if I wanted to.
1) I guess I'm just looking at things differently than most people. I can deal with a remote switch, and run tape switches on all my AR-style rifles without any issues. For me, that would actually be the preferred method over a tailcap switch.
As for a barrel clamp, everything I have come across for the M4 seems to have issues with either not staying put due to recoil, or actually effecting the magazine tube to the point that it does not feed reliably.
2) I suppose if I could find a long enough light, I'd be willing to try that. Assuming of course, that it didn't end up weighing as much as the shotgun itself.
3) I'm in California. SBS is a no go here.
This is very true, and it especially becomes very much a niche market (as you pointed out earlier) when we're talking about an M4 with an 18" barrel. This is also, I think, why it is so hard to find upgrades for the M4 in the first place. Perhaps my general frustration in that sense is increasing my frustration about the light mount as well.
Also, I agree with you in that more options are always better.