I feel as if doing the thing TTT does would be shit as it'd result in having like 1 murderer and 30 bystanders, absolute anarchy, plus it'd end up taking longer than if it was just a regular round. I haven't played the server, but maybe if the first round of each map was some sort of FFA with reduced round time, then it's possibly faster
The system works fairly well on TTT only because everyone has weapons, if you were to do the same for murder you'd have one person (probably 2 ig with sherrif) then however many bystanders just waiting to either find the revolver or get shot. slow as fuck.
Besides, you'd then get the complaints of "I get murderer and it's down to a 1v1 and then suddenly 3 people join and I can't win anymore"