Regarding author parsing I've submitted a pull request so there should be an improvement on that front. Although the feed does present authors in a weird format and perhaps a good way to address this would be talking to espacenet. They should at least not provide authors in all-caps. Do note, that if you drag the item into your library or use the Add to My Library/Collection button in the item pane Zotero fetches correct metadata.

Regarding your second request - we'd generally want more customisability for the item list, but that comes at the cost of increased complexity (both in terms of code and UI) and this is not an often requested feature, so no promises on that one any time soon. We do welcome code contributions from the community if you want to give it a shot.

I guess I underestimated the difficulty in adding fields to the column/sort UI list, since the 'patent number' and 'assignee' fields are already parsed into the database for each cited patent.

This has less to do with the difficulty in adding these fields to the columns elector and more with the fact that there are too many fields to display them all. I am not really sure how the current list came about, but I assume there is some logic to prioritising the fields that are in it. Allowing a greater flexibility would mean adding a more rigorous and thorough solution to show/hide all possible columns for all item types, perhaps somewhere in the preferences pane. On the other hand, exposing too much customisability to the end-users makes the whole software less user-friendly. As introducing this requires significant consideration, yet there are not many requests, this isn't currently a high priority, unfortunately.

My coding skills are pretty weak, and not sure I'd know where to start, but maybe I could maybe take a stab at it...

FWIW, it is fairly easy to write a Zotero plugin that reads a list of fields from a config file and adds them to the column selector.

I am not really sure how the current list came about, but I assume there is some logic to prioritising the fields that are in it.

I think that's attributing more system to the process than justified. IIRC, the current list was proposed by @Gracile with Dan, me, and some others chiming in. I don't think it should be treated as eternal truth. I think broad applicability was a criterion and in that vein, I don't think Assignee (which just exists for Patents) makes sense, but I think Number (which exists for a whole range of item types) does. I think I mentioned somewhere else that I'd be very much in favor of adding that to the "More Columns" list.

My vote would still be for a dedicated Assignee column, as people who rarely cite patents would probably never use it anyway, but it would be really useful for patent people.

But if not, maybe append Assignee to the Creator (Inventor) field. - i.e. "Bartman et al. (Microsoft)" if a cited item has a non-empty assignee field... You still couldn't sort by Assignee, but it would be better than nothing.

In any case I'll take a deeper look at the plugin dev area.

Great, thanks -- that's pretty much how I remembered it and as you can tell not super systematic. I also think the cost of adding columns to "More Columns" is relatively low as long as we don't go crazy.