About point 13, adding a "Did you mean?" feature... this should be done in a way that applies to Biblios, as well, as it has often been requested in that context, and as we see with points 5 and 6, the mechanisms under Authorities are very similar to those under Biblios.

Drawing "Did you mean?" suggestions from the bibliographic database would actually be a completely different animal from drawing the suggestions from authorities. It would require a completely new set of dependencies along with the ability to extract co-occurrence information and generate suggestions from them. By using authorities for "Did you mean?" all we have to do is search authorities, and suggest related terms. Note that the related terms suggestions will be appearing in the bib searches.

I believe a 15th point is required: fixing Authority Types. Right now, they are essentially hardcoded, looking at the presence of specific MARC field numbers, and determining their Auth Type from that (during import, at least). This means that newly created Authority Types wouldn't be accessible unless:

They used a completely new Main Entry MARC field number
The code was edited to associate that field number with that Auth Type
One prime example: right now, LCSH and MeSH subject headings are both of the Topical Term Auth Type. They have the same MARC structure, but belong to different thesauri. As it stands, there is no easy way of differentiating a heading from one thesaurus from that of another.

This may be out of scope for the work you're currently planning to do, but I'd ask you to keep it in mind all the same, and do any development with an eye towards making Authority Types more robustly supported.