I'm on the fence about it. You have the power to set the example and offer ad space on the steemmonsters website, but I don't think I would like to see that as its not a freemium game. On say busy or dtube I wouldn't mind as much.

If it was brought in steem and had messages like 'Trezor, Inc is running a 300,000 STEEM campaign to bring you this message...' then yes it would work for me, but I think the dApp would have to be incharge of ensuring it bring some value to steem as advertisers wouldn't want to go through such a process. Even if it was just something like a commitment that 20% of the fiat from ads goes to powering up steem.