Interesting idea but I really cringe at the thought of taking a unit of Firewarrior purposely without transport just for them to die. We are not the Imperium ffs!
I'd like to point out the difference between our kroot and our breachers. The main driving point behind kroot is for them to die. Yes, they offer deepstrike area denial and they make a mild screen. But humor this:
12 breachers and 16 kroot cost the same number of points. Assume that we've got 18 successful to-hit and to-wound rolls from a spacemarine's bolter. Kroot and breachers have the same toughness. So, as an armor save the kroot pass on average 3. 15 die. 1 remains. out of the 12 breachers 9 die, and 4 remain. You're at a profit at this point if the only thing you're doing with your kroot is using them to die. those 4 remaining are 5.3333 times more expensive than the one remaining kroot (not counting the kroot that die from battleshock).
To top this off, the closer the enemy is to the breacher the harder the breacher will hit them. Makes your opponent more likely to make his charges from farther away, which gives your breachers a better chance of not being forced into combat at all. Doesn't matter if they're kroot or breachers, they'll die in CQC.
Ultimately, I want to say how much I like this idea of breacher screen. It's not some penultimate technique, but it's seems to be very good. The math behind it is nice and the tactical edge of making your opponent concerned about charging from up close is always fun. I ripped 'nids a new one by making the nid player try to make longer-distanced charges.