When a platform vendor puts up restrictions, it can be scary, and with good cause. Microsoft's Universal Windows Platform (UWP) is the successor of WinRT, which, in the Windows 8 era, forced web browsers to be reskins of Internet Explorer, forced developers to get both their software and themselves certified before publishing, and so forth. They still allowed the traditional, more open, Win32 API, but locked them into “the Desktop App”.
Naturally, UWP carries similar concerns, which some developers (like Tim Sweeney of Epic Games) voiced publicly. It's more permissive, but in a brittle way. We don't want Microsoft, or someone like a government who has authority over them, to flip a switch and prevent individuals from developing software, ban content that some stakeholder finds offensive (like art with LGBT characters in Russia, the Middle East, or even North America), or ban entire categories of software like encryption suites or third-party web browsers.
This is where we get to today's announcement.
Microsoft's Phil Spencer, essentially responding to Tim Sweeney's concerns, and the PC gaming community at large, announced changes to UWP to make it more open. I haven't had too much time to think about it, and some necessary details don't translate well to a keynote segment, but we'll relay what we know. First, they plan to open up VSync off, FreeSync, and G-Sync in May. I find this kind-of odd, since Windows 10 will not receive its significant update (“Anniversary Update”) until July, I'm not sure how they would deliver this. It seems a little big for a simple Windows Update patch. I mean, they have yet to even push new versions of their Edge web browser outside of Windows 10 builds.
The second change is more interesting. Microsoft announced, albeit without dedicating a solid release date or window, to allow modding and overlays in UWP applications. This means that software will be able to, somehow, enter into UWP's process, and users will be encouraged to, somehow, access the file system of UWP applications. Currently, you need to jump through severe hoops to access the contents of Windows Store applications.
They still did not address the issue of side-loading and developing software without a certificate. Granted, you can do both of those things in Windows 10, but in a way that seems like it could be easily removed in a future build, if UWP has enough momentum and whoever runs Microsoft at the time decides to. Remember, this would not be an insidious choice by malicious people. UWP is alluring to Microsoft because it could change the “Windows gets viruses” stigma that is associated with PCs. The problem is that it can be abused, or even unintentionally harm creators and potential users.
On the other hand, they are correcting some major issues. I'm just voicing concerns.