I agree that it would've been fitting to have had Alex's final episode air on Christmas. However, I do like how it'll be delayed until 2021 (not pushed back into February sweeps but right after the holidays). As mentioned, the annual NBA quintuple header for Christmas Day would impact several people. Plus, Christmas Eve occupied with their (and other families') last minute stuff, Church, dinner, etc.
I wasn't sure if they would've held off starting production until Season 38, but that's way too much of Season 37 to void. Chances are that a permanent replacement will not be made official until next fall. I don't have a problem with Ken as host. I think it makes the most sense to have Jeopardy start with Jennings. Given the struggles with getting a permanent host for TPIR and Family Feud that worked, I think Jeopardy will be okay going forward with their final decision. If not, they could get someone else, but at the end of the day, they'll get someone that, while not as great as Trebek, will be the man or woman slated to become the face of Jeopardy for years to come