Personally, I think you are on the verge of having this thing ready. I'd prioritize it along the lines of structural integrity (html, forms, logins), user configuration, and administration. Knowing your proclivities, I'd assume that the backend is on a solid foundation, so I'm venturing that you got that sauced - getting the database store & fetch is always the first order of business.

Search: Not important until such time as we get more content.

Parent thread listing above content: Not important for me, since I usually know what I'm replying to.

NNTP Gateway: Will become important at some point, but as long as you keep it in the back of your mind with the current design it's not something we've had in the past so it's not missed.

Mail-on-response: I dislike that feature so consider it very low priority.

Administrative interface: Who cares about adminstrators? Probably important, so do what you must. While we're on the subject, what manner of archiving scheme are you envisioning?

Killfiles: Not something I'm of the mind to use until the S/N ratio gets out of whack.

Show New Forums Only: As long as we have the LRPD to flag the forums with new messages, not important.

Single SQL for forum list: can you explain?

pagination on forum displays: Will become important very soon.

Don't show lrpd for Anon users: Not priority.

Mark forum category read: Not priority.

Collapse forum categories: Not priority.

Alternative nesting spacing on showContent: can you explain?

Factor posting functionality (quote buttons disappearing, etc): Important. What I'd like to see is a lot of those buttons removed based on the user configuration. For example, I never use signatures so I really don't want to see that on my forms. The size buttons probably don't need to be on the form - just a user config parameter.

Duplicate post prevention: Not priority.

Fix CSS usage: Based on the number of different browsers IWETHEY users have, it's probably an important item.

Stats: Later.

User-selectable caching controls for dynamic pages: User configuration setup I would presume. Might be nice to knock this one out of the way soon.

Page titles: I would think that it shan't be too difficult, so I'd have this one as a high priority.

Move authentication to Login Manager: What are the implications?

Alternative nesting spacing on showContent: can you explain?

Some people don't like the use of tables for nesting.

IMO, the best way to do the nesting is to use nested <UL> The unordered list was designed with exactly that purpose in mind - they will download and display faster than tables or arbitrary space constants.

There are two downsides to using lists. First, the original IWE forums would indent too far per each level. I think you could solve that via CSS control over the margins per nesting level in the list.

Second, when the right hand shift came in, the wrapping would occur after practically every word. Perhaps a nobr type of thing to keep the text on one line?

Anyhow, you might consider using CSS and unordered lists as the solution.

...the worst case is probably not those browsers, but earlier versions that think they can but had all sorts of bugs.

I think Lynx will ignore the CSS, but you'd still probably be better off using Lists for the indentation - it'd just look like the original nesting that we had on IWE.

Of course, user selectable methods are the best alternative, as long as the software can handle it. Means you'll have to isolate the features as best as possible, and do some additional testing with the major releases. But since EZBoard never seemed to test things, you have a pretty low standard to live up to. :-)