I hear you. It would be great but, even if it were to be of benefit to Microsoft and therefore possible, it would tie the release schedule of one into the schedule of the other. It would mean the PlatformIO team having to put time and effort into keeping aligned instead of putting their focus into improving their solution. It is not a big effort to install VS Code and then add PlatformIO. It might be a great initiative to make that even easier than it is today?
For individual users, the current structure (PlatformIO as an extension of VSCode) is enough and friendly;
For a small/startup comany who wants to provide his own service to his customers based on PlatformIO (or PlatformIO Core only?), the current structure (PlatformIO as an extension of VSCode) is not friendly.
Yes, alignment of the versions of VSCode and PlatformIO will be of time and efforts consuming. Without the friendly support from PlatformIO, the small/startup comany will has to consider building his own IDE from scratch or VSCode.