That being said, I do think they could've made this work. If you read a summary, it doesn't sound that bad. The thing that really ruined it for me was the forced delivery within two episodes. It just felt like tearing down everything, with no consistent plot or delivery and then topping it off with a bad joke. If they scrapped the actual season 9 and instead made a season 9 and 10 leading there, it would've been totally fine. And they knew this was coming!
Also, on the subverting expectations part: This is totally fine. However, HIMYM is a comedy show. Playing it for a joke is fine, but that was more the "suprise, your mom has cancer!" type of subversion and definitely didn't fit the mood show.
Correct. Almost every single episode of the show from the first one in September 2005 in some way foreshadows the ending. It's, overall, the most coherent and consistent continuity in television history.
(For those who don't want to rewatch the show, I've heard that watching the first two episodes and the last two episodes together makes for a very satisfactory rom-com.)
Part of my change in heart comes from rewatching the series, it seems to me that they had this as the intended ending all along. I also think it serves as an interesting commentary on the notion of love and romantic attachments that Ted struggles with throughout the show.
But overall I am frustrated with the film industry's overall obsession with subverting expectations. Viewers want some sort of payoff, and withholding that can really burn people who've invested time into watching content (especially for long running TV shows). You can sometimes achieve payoff even while subverting expectations, but too often you end up with an incoherent mess.