Chess is a niche. You don't see people campaigning to add/remove pieces or change the board dimensions and get rid of the old game.
I don't accept your premise. Reductio ad absurdum, are you going to say any change is the same as shutting the game down?
If you switch from 6 hour switch timer to 3hr, is that changing the game so you might as well shut it down?
If you rotate maps, is that changing the game so you might as well shut it down?
When we went from 512x512 maps to 256x256 maps should we have just shut down the game instead?
Can absolutely improvements or modifications ever be made to the game again?
Think of all the changes to the games we've seen in AH since 1999. Could you say at each change, it's better to shut the game down than change anything?
I seemed to remember this community being a lot more open to change in the first decade.
Being a niche doesn't mean you can't every change anything. You should always be constantly changing and exploring and trying to uncover the perfect expression of that niche.
Life is constant change. Only dead things don't change.
You've got it right, if he's going to do anything he should just freeze AH3 and create a new game with the gameplay pretty much being redone from the ground up.
I think he should do that:
1. For fun. A new adventure.
2. Financial diversification. Your entire livelihood, retirement, and children's chances at a college education all balanced on the tip of a single point of failure dependent on a population of old geezers with one foot in the bone-yard, is less than ideal.
You can diversify with new games, also by bringing in new blood to your current game. Preferably with teeth. Or you can do both an sleep even better!
That doesn't mean you can't every change anything in AH at all. It's just a matter of how you balance resources. And often, resources can server multiple purposes.