I might buy an M1 Mac now and be able to play games optimized for M1. But in a year or 2, games become optimized for the latest and greatest MX generation. Now my $4K M1 Mac is useless.

I don't see that happening, it doesn't even happen that quickly in PC gaming which is notoriously fast moving. I think it would be more like consoles. Since the pool of hardware is limited, developers can aim at the M1 for example for a few years and then once the market naturally moves on to upgrade in significant numbers they can change the target.

But there's more than just hardware or even porting toolkits like this that are needed for Macs to be core gaming machines. Apple needs to actually care about it for one thing, instead of milking 30% of IAPs until the heat death of the universe.