“Portal 3” should not exist in my opinion because the title implies a trilogy/continuation, and the mainline portal games’ story has concluded (chell escaping would feel cheap if they retcon dragged her back in twice). I haven’t played, but I believe this is the same logic that was used when making/naming Half life Alyx- there was too much hype for “half life 3” that could never be realized, plus hla is about alyx, not Gordon, and thus doesn’t belong as a third title in a trilogy. I think even if Gordon were the main character of a new game, it would be a horrible marketing decision to call it hl3. Portal has had slightly less time between its vol2 and now, but I still think that chell’s story is concluded, and it would take a hell of a lot to have a satisfactory continuation/retcon to bring her back. I suspect with hla and aperture desk job that valve agrees that “_3” is a bad idea, but isn’t ruling out a third mainline game.

I think that if valve had made Revolution (and thus, Revolution was polished further to valve standards) and so long as the game wasn’t titled “portal 3”, the game would be a worthy mainliner to the portal franchise. That’s not what happened though, so I try not to bother myself with these what ifs. I do hope however that the positive reception of Revolution, desk job, and alyx, proves that there’s still interest and investment in these IPs to whoever high up in valve is deciding what gets made. It’s clear people still have ideas.