On the other hand, they've got numerous requests for features that
wouldn't involve duplicating code that someone else should write (and then removing the duplicate code when it does eventually happen) and which have widespread support for addition to the program. They can't do everything, so choices have to be made. Proposals that involve writing a lot of code which will be thrown away later probably aren't as attractive, all else being equal.
You can't accurately assess the amount of support there is for a new feature from looking at the forum postings, because forum postings don't go into the development database, only requests sent via Help->Send Feedback or email to <appname>@omnigroup.com (or by phone, I suppose). I've never heard anything to suggest that CalDAV support is near the top of the most frequently requested list.