I'm not sure if this is something you are considering for actual rescues, or specifically four your divemaster training / activities.
For actual rescue scenarios I don't think it would add much:
- drag is lower when the FFM is connected with only a hose as opposed to connected with a hose and a strap
- FFM drag really isn't that interesting overall, remove tank and bcd altogether and have the victim float naturally, combined with added buoyancy from exposure suit (if used) in order to remove drag and get the victim out of the water asap
- damaging kit when getting out of the water is not a consideration. If it is in the way, it goes. If it sinks, it sinks. If the situation allows for it, retrieve the kit (especially tank, bcd, regs) for any future accident investigation, but if it gets in the way of treating the victim asap, leave it. This includes expensive stuff
- If you design and produce something special, rescue training has to adept to it as well. Just compare a rescue with a jacket BCD with a rescue involving bp + harness. Different technology requires different rescue technique. Luckily, the universal technique of using a proper line cutter works really well...
If it is for your DM course (or during rescue courses you might assist with in the future) you might want to consider switching to a normal mask, as it will take more of a beating during activities like that. Students who get excited and pull to hard on straps, drop stuff etc. Safe the FFM for when you are actually diving. Also check with your instructor on his / her philosophy about using kit that is as comparable to your students as possible. Cases can be made for diversity (broader experience) but also for standardization (familiarity), so keep that in mind when selecting kit you use during dives like that. It can be really good fun to play the victim, but unfortunately equipment will be abused..