by virtue of having players in the room, more players get drawn in, then the fake players spectate themselves.
That already exists and it the most annoying thing ever.
There is always players who think it is a great idea if they wait in "Small Teams" or "1v1" room to seed games. The problem is if someone enters to actually play then they suddendly no longer want to play or are afk or have some other reason why not to play now.
If not willing to play they could at least idle as spectator, but for some reason that is impossible to them. And the few who actually want to play suddendly begin that doing totally unfitting mapvotes.
Once I used to be happy if I saw a player in those rooms and hoped for a game. Now I just join, ask "game?" and if no/bad reaction then I do not lose time with debatte/waiting, instead just leave directly to cluster for quick fun or disconnect.
That behaviour has already ruined every version of matchmaking, because you always got opponents who were afk or unwilling to play.
So the only thing this strategy has "seeded" is annoyance.