I expect that the incremental model improvements will become smaller and smaller until they run into the same diminishing returns effect like all other new technologies (FWIW I've not beeen seeing a lot of difference between the latest Opus and Fable models for the stuff I'm doing, so I just stick to Opus for most things. There's a noticeable difference between Sonnet and Opus though).

I'm not ready to take any bets when exactly the curve will be flat though ;) (e.g. in a just couple of months or a couple of years)