You don't have to argue against it. The documentation is maintained to be released with the next official release. Do not worry about that. It is just that features in trunk may appear and subsequently also disappear.
If a feature is announced, you are usually safe to use that, but not all features ARE announced because they may be incomplete and transfered to the next trunk/main.
There is no way around it: use the git features will do.
Also note that we FPC users are lucky that we can always see the status of a yet to be released version, whereas most software development relies on alpha and beta testers.
Using trunk you are an alpha tester. When there is an announcement for release candidate you can become a beta tester.
If you want to follow trunk, OK, but realize what you are doing. Most people don't (Like Fred)
To follow trunk you MUST do a daily check on the revision and update when necessary and be able to compile trunk yourself. There may be moments that even fpcupdeluxe can't help you.
And even then you may run into trouble if somebody just committed a feature or fix...
<sigh, all this is so difficult to understand? >
Very angry Thaddy.