Ahh, interesting. I can't answer that question. I too, have a machine that could benefit from that notion.
Although judging by MS past. They usually only support the most recent OS as an in-place upgrade qualification. Remember Windows 7 could upgrade Windows XP, but it had to be a clean install upgrade. The same is true for Installing Windows 8, an in-place install is not supported for Windows Vista. I can only imagine Windows 10 will be the same for Windows 7.