Original Sequel Plans - Please Correct Me if I'm Wrong

As far I understood, Valve's original plan was to first release Half-Life 2: Episode 3, which would have effectively concluded the story arc for that particular series, to be then be followed at some point further down the line by Half-Life 3 compromising of an entirely original plot and game engine.

I think it was safe to assume as little as two years ago, never mind now, that Episode 3 was by all intents and purposes a bona fide example of vaporware. Therefore what of the full sequel? Valve are now telling us we'll see a trailer for Half-Life 3 next year but gamers remain sceptical and more importantly do they even still care? I do fear that the brilliant momentum the developers had attained by the end of the last instalment has perhaps dissipated to an irreversible degree in the intervening six years. I realise Valve make superb titles and are also absolutely notorious for their lengthy delays but perhaps they've gone too far on this occasion. Of course I hope I'm wrong but I'm seriously doubtful of even seeing another Half-Life game regardless of whether it can possibly live up to expectations.