Maltrail is on my radar and in my TODO list. I think it would be a great addition to SecurityOnion. I haven't played with it yet, but had requested a couple of changes that will allow it to play nice with other sensor-type apps (eg. it no longer hogs all CPUs in multi-thread mode).
It has a server/sensor/standalone architecture similar to SecurityOnion, and its python-based HTTP server could be proxied by apache2 just like ELSA is. It uses UDP to push alerts from sensor to server, and http from sensor to server to pull new threat intel down. That could be adapted to use Salt if someone wanted to go through the effort..
It's under heavy and active development, and has a good collection of feature requests from a variety of users. It may need to mature a little, as the first release, "Borg Queen," was just on January 5 and in less than 2 months there have been more than 350 commits on top of that. Keeping up with the latest changes would take some effort in packaging and testing.
I'll update the list with the results of my testing once I get a chance to play with it.
I'd be interested in evaluating this as well :)
Thanks,
Wes
Any more info on if this will be integrated in the future?