Counterpoint Research's latest study of the 5G market in the US has found that sales of mobile devices that can use these new bands have been detected in more than 10 cities. However, some of the areas in question still do not have an actual next-gen service. This phenomenon has been attributed to consumer interest in future-proofing.
https://www.notebookcheck.net/5G-phone-sales-are-on-the-rise-in-numerous-US-cities-even-those-without-coverage.427408.0.html
Taking into consideration that most 5G sold today aren't 100% compatible with true 5G SA (all current Snapdragon 5G is NSA and cannot be used in SA mode), I don't think that it's very "future-proof" to buy pre-5G tech today. Better off getting a better 4G today and a true 5G one when SA is deployed.