Advertising on steam - yes, that could help.
Playing with / though steam - well, I think HW is not the right type of game for steam.......too complex, steam games tend to be launch and play, bish bash, crash, wallop..........which HW is not.
There are many 100s [maybe 2,000+ ???] of people who have purchased HW already, where are they for MP games, steam will not get them playing if they don't want to play now.
Steam might get some new people interested, but if the first 2,000 don't want to play MP why will the next 2,000 want to ?.
I wish I knew the answer to that.
This is as near the answer as I can get :
A "special" HW only, built for purpose system, would be the best option, if only it were practical and cost effective to do.