Well as I said, the main issue is if we don't want to break all links through the 228000 posts on the current board, then we have to make the old posts so they have higher ID numbers than new ones, and this is where the problem arises: SMF appears to sort topics by last reply ID instead of timestamp. The author of the Custom Board Sort mod claims otherwise about his mod, though, so maybe it could be solved with that (Juju would need to check if we run the latest version). Merging by itself seems like it might be easier, since the instructions are available somewhere on SMF site, the problem is just choosing between having all old posts appearing above most of the new ones, breaking all post links like what happened to United-TI two years ago or writing/modifying an SMF mod.
It would be really great, though, to have all old posts merged here, all sorted into the current categories. The projects and ideas board would end up having over 65000 posts too