They wouldn't have to give up any major channels of revenue. This would just be an improved architecture for their existing micro transactions, that also enables a secondary market.

Remember that NFT contracts can be written such that the original issuer can get a piece of secondary sales. That is a new revenue stream for the content owners.

I think that interoperability will not be universal, but maybe you can buy NFL gear on an NFL website and then it happens to also work in the licensed NFL games -- stuff like that. Or Nike negotiates with Fortnite and Roblox and Minecraft so that Nike NFTs that you buy from Nike.com work as avatar customizations in these games. I think this is how it starts -- limited and negotiated interoperability between non-competitors. Maybe it gets to where competitor games have interoperability, but that is definitely not where it starts.

How would I use an item from world of war raft in another game?

You can't even use items from D&D 3.5e in D&D 5e.

I think that interoperability of functional items, rather than apparence items, needs to be careful considered on almost a per-item basis.

There will not be universal interoperability of functional items across disparate games, and only limited interoperability of functional items within game families/series.

Royalties are not supported by the existing nft interface. They are instead done by services like opensea.