If you were talking about Go, which has a winner in almost every game, then the discussion of ever-increasing ratings would make sense. But in the context of chess, the conversation runs into the rules of the game.
If you ignore the nature of chess, it's easy to create a scenario with almost any Elo rating.
What rule of chess am I ignoring? The 50 move rule doesn't apply when it comes to engines.
I assume he's pointing out that in go draws don't exist and that in chess draws do exist.
In go even if you play imperceptibly better, you win. In chess you have to outplay your opponent by a fairly large margin to win.
What if a new computer program beats a 3600 9 out of 10 times? Wouldn't the rating have to go up?
Weak amateur human games end in a draw maybe 1 time out of 100. As the players (human or computer) get stronger, the draw rate increases. From memory (so it may be wrong) Carlsen draws about 60% of his games. Top engines can draw each other >80% of the games.
He's saying current programs are pretty close to perfect, so even a solved version of the game (a database that merely looks up whether a move is winning, draw, or losing) wouldn't be able to score 9 out of 10 against current engines.
As I have pointed out before, rating differences still lead to the same scores by definition. The difference is that the stronger player loses less and thus doesn't need to win as much to achieve a certain rating difference.
Some top computer matches have seen the extreme version of this, where all the wins are by one side.
What I mean by increased draw rate is, lets say, increasing ratings by 100 point steps.
1000 vs 1100 in a 100 game match is expected to score ~64%
1100 vs 1200 [ditto]
. . .
3400 vs 3500 [ditto]
But at each step, while 64% by the stronger player is maintained, there's a higher % of draws in the composition.
So the argument is increased playing strength will have diminishing returns, because results are tending towards 50%
All of this I'm sure you already know, but just to clarify what I was saying.