As the lead behind the holiday content, this hit me pretty hard too. We put together a lot of great stuff for you, and in the case of Shade's Eve, our design work was practically done. (Winterfest, in its frozen state, is a rough li'l slice of wackiness.)
Ultimately it was put aside because we, as a company, are focused on making the next patch as free of bugs as we can possibly manage. That means testing... a lot of testing. We have finite testing resources -- any company does -- and so the choice had to be made between including the holidays in our testing and thus having the content as a whole -- all of Drop 3 -- get less testing, or excise the holidays and ensure the other content, the content that would be permanent, got more. As we're committed to that quality bar, the limited-time holidays had to take a back seat.
I totally get that you might want to see decorations and costumes for the holiday, particularly as you know they exist. The problem with that is that it would still require more testing than you might think. The city decorations, for example, are not spawned in like they might be in other games, but rather operate on our plug system -- very similar to housing. This means that the entire area of both cities was sliced into sockets that then get holiday decoration plugs put atop them under the right conditions. However, unlike housing, there is a huge mess of NPCs and scripting afoot in the cities, and their interaction with those plugs requires a lot of testing on their own merits.
Even something as simple as putting costumes on a vendor -- bypassing the reward structure we had all baked into Shade's Eve -- would require testing to make sure it's selling the right things, that it'd show up at the right time, that it would clean up after the holiday, etc. All of this testing is time away from ensuring the quality of Drop 3 and could introduce new bugs (edge cases are fun!).
Believe me, I would like nothing better than to give you all of the awesome stuff we had cooked up for the holiday season this year, but practicality and priorities dictated otherwise this time. I hope you'll enjoy it when it does come around.