Xbox One games often require an online connection to work now, which is essentially DRM. Other than that, purchasing anything from the Xbox Marketplace adds it to your purchase history, which you can access at any time to download even de-listed items provided you downloaded them when they were previously available.
So, I believe Microsoft's system is capable of at least verifying all digital purchases of games or DLC.
Also, as I have mentioned, plenty of other games have allowed for free upgrades and save file transfers, so it's all very possible, if nothing else.
This is no criticism of you, Leonardo, but more generally speaking, the only issue in my mind is whether people care enough to oppose the decision by Bethesda. I knew full well that the Skyrim forums would be populated mostly by PC gamers, seeing as the game ran it's course on consoles a while back, and that many would vehemently oppose a backtrack by Bethesda to take away their "free game", though the current reception has been mixed and those that do agree with me are only tentatively doing so, due to the crowd mentality set against me personally.
I'm more than happy to wade into this particular mire where my opinion shall not be popular, but if we could refrain from the indirect snipes on my character in an attempt to undermine my argument, that'd be great.
Keep things factual, free from speculation without substantiation and preferably civil.