Perhaps it might be a good idea to let site users organize their own mini-conferences/meetups somehow, using the Stack Exchange engine. Especially if you consider communities that spread across sites. As a simple example:
- Software = Stack Overflow, Programmers, Game Development, Code Review, IT Security, maybe SQA, maybe UX, maybe CS Theory, many users of PM,
- Science and Mathematics = Mathematics, CS Theory, Physics, Crypto, Astronomy, Statistical Analysis
- Art and Design = Graphic Design, UX
- "Liberal Arts"/Humanities = Writing, Literature, the various language sites,
- IT = Server Fault, DBA
- Engineering = Signal Processing, Electrical Engineering, a few other proposals
- Power Users = Super User, Apple, Android Enthusiasts, Web Applications
A good starting point might be the Area 51 categories of Arts, Business, Culture, Life, Professional, Recreation, Science, and Technology. Those are rather broad (I believe both Programmers and Signal Processing are in Technology, but as a software developer, I'm not interested in signal processing, but I'm sure those that are would be involved in the signal processing site).
It's probably a non-trivial task, or even something that has to ultimately be human driven, but if you create tools to let people organize meetups with people with a similar interest, it would achieve some of the same goals of DevDays of collaboration and learning on a far more frequent and local basis.
The only problem might be some smaller sites or grouping of sites that don't have a lot of traffic or users getting meetups off the ground. But the way that I see it is if you enable two or three people to connect off-line to meet, share knowledge and information, and even socialize a bit, you've succeeded.
So far, there's been no comment or answer from anyone on the dev team. However, I also see that (thanks to a comment) people who were planning on attending the London Dev Days are using Meta.SO to try to organize another event. I think that's pretty nice, but they are going to miss out on a lot of people who don't browse Meta. So is it the current practice to post on Meta.SO (plus any Metas from relevant sites) to try to organize events, and is this the best we can hope for in the near future? Does the SO team endorse using Meta.SO and other Meta sites for organizing meetups to replace Dev Days for people who took the time off and arranged travel? How about for locations that weren't scheduled for a Dev Days?