In theory yes. In practice that might work that way if ~5% of your users are in that situation. If ~50% of your user base is running on a legacy protocol and you're running into Churn risks, the company is going to re-evaluate if they want to retire the old protocol.

There _is_ a reason even legacy cable TV and ancient DOCSIS channels are still being available in many countries because actually retiring a lot of old modems has shown to be risky to the business.