Structurally things haven't changed much, but it's not that long ago that it got a new theme (the current one, prior to that it was the stock PunBB theme). Two years?
I actually prefer PunBB, but a large part of that is likely to be that I was relatively new online when phpBB was in its prime, and PunBB feels a lot like a cleaner phpBB. It looks and works like the first web forums I got used to, so it feels natural. Functionality wise I get by with Discourse, but as a user I don't see major things I really like that PunBB doesn't cover. A regular mention is PMs, but a PM-less forum has its own advantages - no reason to discuss problems and solutions where Google can't read them, and getting messages somewhat related to a random post from several years ago just isn't productive.
Visually Discourse leaves a lot to be desired for me. In particular I have serious issues telling posts and quotes apart, where a quote a lot of the time can look like the start of a new post and vice versa. I'm not familiar with Discourse theming, but I might look into that at some point to improve contrast, especially if it ends up being the preferred forum.
Note that my comment is purely an answer to "which software do I prefer", not which content base I wish to move forward with. From my perspective it never seemed like the OpenWrt forum got attention similar to what the LEDE forum has received, so comparing them based on content organization, moderation and cleanup isn't reasonable, or important. Maybe Discourse has better administration tools, which is a worthwhile point to bring up for those who can provide input.
I personally have experienced several situations were PM's on the OpenWrt forum would have been extremely helpful, else a user really only has two choices... post a reply about something somewhat off-topic, somewhat on-topic, and hope the user it's aimed at is reading all new posts, or create a new thread, but since there's no mention functionality, that's not even a viable option... this in turn leads to cluttered threads.
Cluttered threads lead directly into a lack of thread search, of which is a disservice to all, and of which does result in threads ballooning exponentially (there's no rational reasoning to a thread having 14,890 posts due to lack of thread search)
PMs wouldn't be important at all if the OpenWrt forum had mention support and mention notification, along with thread search. For example, GitHub doesn't have PM functionality, but does have the aforementioned abilities.
PunBB 1.4.4 has been released
Version 1.4.4 offers: support for php 5.5, 5.6 and bug fixes. Posted on 2015-10-14
That alone should disqualify it.
I have no particular love for Discourse, really the main features I care about are pretty standard: Let me sign in w/ 3rd party Identity Provider (Github is nice, but why not Google/MS/Facebook?), subscribe to threads, get notified to replies, either individually or digest style.
The current almost all-white theme is not nice to my eyes.
When I discovered discourse a year ago, I was flabbergasted, that forum's could be this beautiful and functional at the same time. The responsive design works amazingly on mobile and desktop.
All other forums seem to have awkward reply forms, while you can just minimize it in discord to read other comments and while bold/italics/etc. are hidden by default.
If it's just about the choice of forum, then my choice is downright discourse. If it's about politics or previous accounts/threads, then I don't have a clue, what would be better.
not supporting screen readers is a downside, but none than can't be fixed by discourse or so.
E-Mail is no alternative since you can edit posts imho.
better software support, updates, features and modern design are all advantages of discourse though