As predicted several times in the past, Microsoft has finally taking the step of locking down Windows 10 to Windows Store applications only. It is currently only enabled on Windows 10 S, however there are good reasons why Microsoft may choose to make this the default Windows 10 configuration some time in the near future.
By restricting installs to Windows Store apps Microsoft gains two things: control over the way apps work when installed in Windows and control over the security of the Windows platform through keeping the malicious programs out. A more reliable, more secure operating system is what everyone strives for.
However Microsoft has some work to do before it can consider taking this path. First it needs to persuade more publishers to brings their software to the Windows Store. Once, and only once, those gaps are filled Microsoft has half a chance of making this play stick with customers.
There's more than a little work still to do on app quality, getting rid of the garbage and ensuring that quality apps, whether they be first or third-party, aren't hidden behind a layer of we wrappers and other hare-brained attempts to bring holdout applications into the Windows 10 world.
Once those issues have been cleared it would make sense for Microsoft to go down a softly-softly route with the Windows Store. Taking the Apple option of restricting installations to the Windows Store by default. Giving users the choice of how restrictive they want things to be will go a long way to avoiding the negative response that previous decisions like Xbox One restrictions and Windows 10 forced upgrades have caused.