If you reverted ownership there's no way that FB are going to sign that contract (a small risk you could inadvertently lose the asset and the cost price, eg through an unforeseen loophole that favours the seller - lawyers should veto such things, surely).
Also, are you going to make it a perpetual term applied to all future owners? If not then FB can probably make an entity to sell it to. Or use a third-party login that itself requires Facebook login and workaround your selling constraints.
I like the idea of it: just practically I can't see how it would be workable to technically constrain a company in a contract of sale of that company.
Are there examples of where this has been done successfully?
Yes. In short, you expressly identify in the contract that the provision is for the benefit of Oculus Rift users, and then they gain the power to enforce it as “intended third-party beneficiaries”.
The examples I can find [there] don't seem to bear much similarity to this situation at all.
It's entirely possible that FB would have balked, but that in itself would have been a useful data point that indicated that they had every intention of bundling the two products together.
In any case, the topic at hand is not so much whether such a deal could have been structured to work, but whether there are any circumstances short of willful ignorance where the founder could have made the promise he did in good faith. I don't see any.
Well, they don't have to. He could have insisted on writing this condition into the acquisition contract. But he obviously didn't. The most charitable reading of this is that he was just naive and didn't know that this was an option or that it would be necessary in order to enforce such a promise, but that seems unlikely. Acquiring this knowledge is no harder than posing the question to his M&A attorney. Hence...
> I absolutely do not t respect yet alone absolve him of not doing so originally. Why would one?
I think you made the right call here.