The arc suppression chamber works best in a certain orientation. Remember the creepy electrical arc in the background of the mad scientist's laboratoratory? It arcs upwards (hence the name), based in part on the heat of the plasma. That arc, if generated inside a MCCB, rises into a chamber that immediately snuffs it out. So orientation is important.
As to MRBF fuses being ABYC aproved, absolutely not. MRBF fuses might be ABYC approved if apropriately used given the fuse's limitations (which for LFP batteries is quite limited). Class T is often the next step up. Still not ABYC approved in every application.
There is really no reason to believe that MRBF fuses will improve in the future such that they will have a 500A rating or a 20k AIC. There is only so much that can be done in a space the size of a sugar cube. Can a fuse that size have a rare earth magnet arc suppression chamber? No. How about a thermo-magnetic interrupt? No. If such electronic wizardry was possible, why not make the little ANG
fuses 400A and 20k AIC? Turns out Bussmann knows that it can't be done.* Same with BlueSeas MRBF series topping out at 300A and 10K AIC. Size matters.
* Turns out some of those little ANG fuses have a 10,000 amp interupt rating, but only for 125V AC. AC is easy.