"We" already have the people working on it. They are just currently backporting stuff, and are actually _replicating_ a huge amount of QA and engineering, because they are the only ones testing that particular combination of patches.
If the same - probably less, overall - effort was piled on top of upstream, there's absolutely no reason why that wouldn't work. I clearly didn't say to "roll your own"; there's value in paying someone for this, because it allows them to specialize, and will be there to support users in case something goes wrong. (And also take the responsibility.)
I completely disagree on the "inevitably". Clearly, this is not the case - it doesn't get frozen forever, because every so often, the enterprise vendors do rev up the kernel. And because it only happens so rarely, it is a huge effort, at which time a lot of problems are found. (Because they crept in when nobody was watching.) If appropriate diligence was instead applied to the on-going releases, there's no reason why a smooth, incremental path wouldn't be available.
There's no reason why the latest upstream shouldn't be supportable. In fact, the pool of engineering on it would be even larger than for any current enterprise distribution.