I don't ever see a chance of standardizing the "ar308" because many companies are getting profit from both AR10 or LR308 platforms, such as magpul for example who has parts for both. Or individual companies keep business by making it so their parts only work with their rifles (or maybe just fewer companies), such as rock river arms, who is great but there is trouble when it comes to using many parts from other companies. AR15s were only standardized because of mil spec from the military, although there is also commercial too, and there are other companies that make their own specs, so there is no true standardization and some times you got to do little modifications to make parts work if they weren't meant for your platform.
If your question is basically you trying to get an answer off of what platform you should build off of, thinking of which platform will be easier to get parts for now and in the future, my suggestion is to not worry to much on that. My suggestion is find an upper and lower matching receivers that you like and fits your budget and just go from there.