Project Centennial is the codename for a bridge Microsoft have developed so developers can repackage their exe, msi and other desktop apps as “appx” packages similar to Windows 10 store apps. The binary installer file gets converted and it will be possible to distribute it in the Windows Store. It can still be available out of the store too as both appx and exe installers.
I do not know about the terms and license agreement really but I guess it is possible to put the app there without restrictions. Just Microsoft checks the app to approve it is malware free and usable .