I will love to see multiplayer games.
this is a very good suggestion.
but it only benefits the players not the owner of the dice site.
if i am not mistaken primedice use to have a p2p game where you could invite another person to bet against you but they stopped it and removed the option from the site. i think it was because of no house edge there and no profit for the site.
Multiplayer in Casino only could be done with proper matchmaking, because there is risk of players working together and exploiting the system somehow.
And it is as you said multiplayer dice not really benefit the House, unless casino will tax games or withdrawals/deposits somehow which can be pretty interesting if it was something like 1%.