yes thats how i would like it, because there always are some players who will leave when this kind of mode get chosen by the host, without telling the players so (before game start). or maybe the last 2 players who joined the game won't know it, till its too late. anyway, if only the host decide all, there could be some leavers at the beginning...
also, u would use a "get host" script, or not? if not, who would be set as host? red? death knight? well, hard to choose without script, cause then, the host will need to pic exactly this position, even if he doesn't want to play on the team.
but maybe adding some kind of ingame command for picking up a random hero. if u type in "-random" then u will get a random hero 10 seconds after game start. as some kind of bonus you could get +10% exp gaining, +10G per intervall or something like that. then everyone except death knight would be able to choose without limiting the other players. on the other side, perhaps for each random hero, the death knight could get +1% exp gain and +3% on all 3 attributes, or something like that. just a suggestion.
anyway, as told before, yeah a vote for all would be fine in my opinion. ;-)