Hi Tony,
I wondered how you were getting on with this project. I also had a need to use tiddlywiki on a corporate (read Office 365) SharePoint server and find in its current iteration it works pretty well.
Im using stand alone tiddlywiki files renamed as .aspx and these launch in a full frame rather than being wrapped in SharePoints controls.
I occasionally get a XMLHTTP 500 error on save, which is annoying. I wondered if you had seen the same thing? I wonder if it may be due to conflicting saves?
Regarding your list of possible enhancements I would be really interested to see how you are progressing with these - especially embedded forms solutions.
Hope it is going well. This really is a very pervasive use of tiddlywiki on SharePoint in a corporate environment. Versioning on SharePoint also makes it very robust.
All the best,
Geoff.