I can imagine just the opposite outcome from the same scenario: as people settle into their favorite but commoditized models, competition for marginal inference cost will take over. A company like OpenRouter that promises the cheapest tokens by the minute becomes essential on the low-cost margin.
I think that OpenRouter and equivalents get pushed out of the market only if the froth calms down (as you posit) and winning models stay proprietary, perhaps with their own unique API surfaces.