Well, I don't think that Microsoft will venture into smartphones again in next 10 to 15 years or at least as long as Nadella is the CEO. He has put so much effort in getting rid of anything that links Microsoft to "Mobiles", I doubt he will have a change of heart now when his efforts are actually showing results.
The best you can expect now is to get 4G or 5G calling activated on Surface Go so that you can use them as mobile phones but with a disadvantage of app gap!