Does anyone know if Microsoft plans on offering an upgrade from Vista to Windows 10 without having to reload everything?
Windows Vista users will need to clean install Windows 10 .. or upgrade to Windows 7 and then get a free upgrade to Windows 10
Not sure it will work, just could try to use an Windows 7 DVD or bootable ISO and change after booting the the Windows 10 TP DVD or ISO and start the install from there while chose Update instead of clean install. It's maybe possible that those will works, like you use an Update DVD or ISO without to have the needed old OS installed. Again, I'm not sure and never was try on my own, it's maybe worth a test and if works, fine!
Related question: How can you upgrade Windows 10 Preview Core Edition to Windows 10 Preview Pro Edition?
go to Settings, Update & Security, Activation, Change Product Key and enter a Pro Key. it will upgrade you from Core to Pro