http://www.marclaidlaw.com/epistle-3/
While the names of people and places have been changed, Its pretty convincing. Considering we're 10 years plus from HL2:E2, you can just hear Valve's NDA expiring. You can find the HL universe names in the story here:
https://github.com/Jackathan/MarcLaidlaw-Epistle3/blob/master/Epistle3_Corrected.md
Its a good read and provides some closure to the series we've (at least I have) been looking for (while still leaving it open-ended). However I don't believe we will ever see anything Half Life from Valve at this point. HL3 (Episode or not) has transcended to a new level of hype that no one at Valve wants to attempt to create. I've read rumors that no team at Valve want's disappoint their audience with something they could never live up to. The writer summarized that as much from his first and last paragraph of the story:
Quote
I no longer know or recognize most members of the research team, though I believe the spirit of rebellion still persists. I expect you know better than I the appropriate course of action, and I leave you to it. Expect no further correspondence from me regarding these matters; this is my final episode.
That's it boys, no more Gordon Freeman. Its going to be left up the fanbase now - you could probably find some community project that's attempting to get the ball rolling. Valve has transcended single player story lines, and has moved onto competitive games like CS:GO and DOTA2 and micro-transactions galore.
It was a pleasure gentlemen. I'm going to spend some time re-playing the series over the next few weeks. Cheers!
