Of course you have the FAs. My point being that the pax to cabin crew ratio is so skewed, not to mention having most of them still inside the cabin during an emergency evac doing their job, that there's few if any people outside the aircraft to manage the large number of pax, especially when the situation is chaotic and not a "vanilla" evac (whatever that is

). It's great to try and do, don't get me wrong, but in practice I would think it darn near impossible for the cabin/flight crew to manage, even with their best efforts.
The large CFR rigs top out at about 65-70, but aren't often driven that fast even during an emergency, as they have to severely slow for turns and have great rollover potential. It's been done more than once.
And problems with CFR aren't new either, and not just with the equipment such as in UA232. When UA 811 was returning at night to HNL after an explosive decompression out over the pacific, there was a near "high" speed collision between a responding City of Honolulu airport fire dept CFR rig, and a USAF CFR rig from Hickam AFB, as both were speeding to their staging points along the runway. USAF rig was hard to see as it was painted dark olive drab green (as all PACAF vehicles were), as opposed to the lime green that mainland vehicles used and the HNL FD vehicles were using. Following that incident, reflective striping for the OD green vehicles began making a large showing, with a black stripe by day, that reflects silver at night.