I think "sux" is a little extreme here. Sure you're going to get some limitation to the amount of droop. But droop is only half of the equation. Granted it's marginally the more important half. The OME springs compress REALLY well. We're talking about a lift that generally runs a little more than 3". Yet it does not use any bump stop extensions. So the Flex is pretty good. The droop is not so good.
Also keep in mind that if you intend to run 35" tires, don't look at the OME like it's a 3", or even 2" kit. Considering that it does not have any bump stop extensions, it's the same thing as running no lift, when fully compressed. I've been thinking about coming up with a mod kit for the OME lift, that would allow 35" tires. This would included a shock mount relocation kit, bump stop extensions, brake lines and coil spacers. I've not run the numbers yet, but this setup may produce some impressive RTI scores.
OK, "Roughly stock wheel travel" then.
I agree with the SL's in general not really being a good way to mount larger tires,as they just raise the ride height...and a good compressing coil, the kind that also gives a nice smooth ride, etc...to me, means that a better approach to fitting 35's on compression would simply be a BL. That would avoid up-travel robbing bumpstop extensions, and, if the shock compressed enough anyway...no stop extension would be required.
Figure the stock arms (Disco'd) limit you to shock travel of ~ 16" fully compressed, to about 27" fully drooped (~ 11" travel shock...)...and to get that travel, all you have to do is unclip the wire and brake lines, diff breathers, etc...and let it go to full extension, then re-clip them in the new locations that allow a more direct route. (So ~ 16" to 27" range shocks...)
On full opposite stuffage (One side drooped/one stuffed), the inside tire edges will be hitting inboard components...so some wheel spacers or rims with less BS would help improve articulation as well.
With the front disco'd...and a set of longer rear sway links to allow the rear to flex better...I think your kit would be a low budget RTI champ....and truly capable of keeping the tires on the ground through the twisties.
I think coil spacers and bumpstop extensions would hinder RTI performance, as you need more droop if you take away uptravel, to get the same overall distance between the tire on the ground, and the one up on the rock or ramp, etc. (Well, the coil spacer approach would be ok in of itself, if the coil can still compress enough etc...)
Shock relocation brackets, if the intent is to use a shorter shock to be able to droop the tire lower, works only if the shock can still compress enough on uptravel...otherwise, it would require up travel robbing bump stop extensions, etc.
Longer brake lines may not be needed if the existing ones are re-routed...the wires are also involved if longer runs prove to be required by new found flex, etc....so longer wire runs would probably be needed if longer brake lines are needed.
So - overall - to take advantage of those great stuffing coils...don't limit stuffage....maximize it, as, as you pointed out, stuffage is half the battle.