Okay so I finally got to test it with a windows 8 box and.....
it died.
typical. so it would indeed need the patch first outlined by Kryxan a few posts ago then rebuilding. It's CMAKE, I'm not up for that ... so IMHO it will be a case of finding something else in the short term as there are quite a few options, or rebuilding one of these things with the new options in them.
I already build rdesktop from source so if you/me can find a windows 8 patch for that - I would consider putting that in the rebuild
probably least resistance. Was good to have a dig around and see what was out there anyways. Happy with rdesktop TBH at this point now, considering the rest.
might have a look at vinagre - but I'll check what it calls under-the-hood before I waste too much time on it.