Right now, plugins in aux/plugins/* need to be build and installed manually. That's fine for those currently there (netmap, elastic search, data series), as they are quite specific. However, once we start moving more standard functionality over into plugins (say, GeoIP support), that will get more cumbersome, as now everybody wanting that stuff will need to do the additional step, which is easy to miss.
However, it's not clear to me right now what's a good way of integrating the plugins more tightly would be. We could turn a few (or all?) on by default and build them along with Bro if their dependencies are satisfied. But that's tough to implement, as the plugin build process is really completely separate from Bro's. So we would need to pass configure parameters over, run their builds, run their installs, run their tests, and catch any errors along the way.
I'm setting this to 2.4 in case we can still come up with a good strategy here. But more likely this is something to punt on right now, as we don't have a pressing use case anyways. There's also the related topic of a broader notion of modules that a future CPAN might manage, and how we combine all that.