actually ...
... there is one way I would support (as in : happy to use) Windows Universal apps. That would be:
1) app store independent of Microsoft
2) easy to switch to and from for Windows users (no need to look for side-loading switch)
3) source code available for all distributed applications (does not have to be GPL - MIT BSD Apache etc. are just fine)
4) no dependencies on closed source libraries/plugins
5) all applications can be easily rebuilt by the user, with free Visual Studio community edition
In other words, make it similar to repository of your average Linux distribution.
Biting the hand that feeds IT
