I doubt that will be a problem. Models are different enough right now. If you can write a spec with enough detail and constraints today to get valid and comparable output from say GPT-6 Astra, Opus 5.5, DSV4F, Kimi K3, GLM 5.3, etc... Then I think there's a good chance that whatever SoTA coding LLMs everyone is using 3 years from now will also be able to implement that same spec.
Again, I think it heavily depends on if people are writing comprehensive specs with sufficient detail.