Is it feasible for a Massive Multi-Player Online Game, such as Honor of Kings or Fortnite or Roblox to be developed and hosted/streamed on ICP and be cross-platform playable including console and mobile?
On public subnet, not likely, BUT can be done on Cloud Engine, 3 nodes should be fine.
How would one attempt to achieve the deployment that way?
You can read about it here OpenCloud.org.
So actually, an entire website could be hosted this way also?? And just 3 high-perf nodes could handle millions of gamers simultaneously?
Very few if any mmo has millions players at same time. Even if you look at Top War, new server can handle about 500 players total. Combined all servers, max 1k-10k online, so people dont need to aim millions. Most loading to client side, server handles you know what logic.
I dont think MMO is right fit on blockchain, it can be used to save some needed data, backup, token item economy.
ICP should focus on easy to build apps that users own, transfer ownership, CaffeineAI is definetly not aiming to give us that.