This is an effort to get some discussion going.
I remember starting grad school and coming across reddit posts with themes like, "What research area will be hot in the next 10 years?", etc. In retrospect, the comments there were not very informed (talk of graphical models and bayesian non-parametrics). But, the heart of these posts is talking about a research area that you find exciting.
So, tell us what research area is currently exciting to you. Are you starting a new job, project, or graduate program to work on it?
To be honest, I won't really miss any specific subreddit. Many of the niche and hobby ones that I cared for, I would not subscribe to, because of the low-effort posts.
I will miss site:reddit.com most of all.