[non-]

You definitely still can just show up and do cool hacks.

Also hackathons are really easy to host if you keep them under 50 people. All you really need at that size is a co-working space and some pizzas.

So if you don't like the vibe at your local hackathons, why not host your own one weekend?

I think the key is really the size of the thing. Giant hackathons with big sponsors and prizes are always going to be more "serious" feeling than your local self-organized hack-days.