Anyone have a copy of what the Reddit post actually said or is that still the same thing that Thurrot discussed and semi-debunked?
Various 343i devs said that they really wanted to own up and fix their mistakes, but they were likely not getting the ressources from MS. Heck, they weren't even allowed to comment on it for a while, not even the Franchise Director and that means something.
With the Xbox One X and various improvements to API's, toolkits, things like "intelligent Delivery" and etc. they got the perfect opportunity to approach it again. I'm also fairly convinced that Phil Spencer's visit at 343i had something to do with it, too, but that's pure speculation on my part.
Either way, it's really really good that they acknowledged the issue and ultimately fixed it. Pretty good to see that they actually have a dedicated team to still work on it and deliver some good updates. It really means a lot to Halo fans and hopefully 343i/MS/Xbox have learned that they can't just half-ass a franchise like Halo anymore.