What if the Bitcoin community could get consensus on building another chain, let's call it "The Miner Chain", that's merged mined with Bitcoin to continue incentivizing the miners through the "Miner Chain" with block rewards, for them to keep securing the network?
Then, it would be the same situation, as it was with NameCoin, that produced completely separated coins, that were not connected with the main chain. Unless people deploying such things would make it better this time, and fix NameCoin's mistakes.
Would that be a possible solution?
Yes, if deployed correctly. And I think people are better at discussing things, than they are at writing code, and checking for themselves, what is possible, and what is not. And as long as this is the case, I don't expect any deployment related to tail supply in the nearest future.
Or would it just be something that could make some problems on the incentive structure?
It would create problems, if not deployed correctly, exactly in the same way as Ordinals created many problems, that some people try to fix now, by proposing LN-based alternatives.
What if, instead of a Tail Emission or expanding Bitcoin's coin supply, Ordinals and the demand for block-space it brings would be the answer to the question, "Will the fees be enough to support the miners when all the coins have been mined"?
You can always raise on-chain fees in many different ways, for example by uploading a lot of data. But then, if you won't deploy anything, that would help on-chain users, then they will pay for that misuse. If you won't give them cut-through-like features, to fight with congested mempools, then you will see gigabyte-sized mempools, or even terabyte-sized mempools. And then, on-chain fees will be high enough to provide security budget. But at what cost? And is it worth it?