I originally started this thread as a slight plea, but would like to make it more useful than that. We've already got a UBB exporter/import "plugin".
I've had a look at converting it to work with other forum software (in my case Simple Machines), but it's way above what I can fathom. Now I noticed that an old user on here (@adarqui - inactive) ported his SMF forum over to nodebb successfully and was planning on posting how he did it, but I've not found that, so I'm assuming it didn't happen.
Perhaps we could get some sort of exporters guide for each forum software going, or if anyone fancied having a go at making plugins for exporting the data, this would really help bridge the gap stopping people from jumping over to nodebb.