Hopefully it'll be at least some time before the make such a big change to Mail.app. Remember it worked well for many releases before we got into the current situation.

People should probably use operating systems written by people who care about backwards compatibility. Ideally ones that are developed in the open.

If I am understanding the problem correctly...

Apple implemented app signing by default in 10.8. Users can either turn this off in System Preferences (removing the error), or the LibreOffice team can pay the $100 annual fee to get a properly signed app.

Actually, there's a temporary workaround which you can use and works till you update to a new version (works with any app or package not signed with an Apple ID) Simply right-click open and you'll not see the error message. No need to disable gatekeeper in System Preferences

That's correct, or users could use the right-click workaround.

Most users, however, won't know this workaround and it shouldn't be necessary to lessen the security of OS X just to use (or update) LibreOffice.

I'm sure the Document Foundation could afford the necessary app-signing.

The GPGTools team had a paid version (beta) out for months. I felt the functionality was worth the minor investment and also ensured that there was some path forward for future revs.

A beta version is nice but it's a beta, i.e., it's not thought for use on productive systems. Paying is fine too but there're always developer releases of OS X and the GPGTools developers should therefore to get their app ready on or shortly after the release of a new major OS X version.

At the same time, I assume that the developers are well aware of the delay issue. So what exactly causes the delay? Is there any way to support the GPGTools developers in this regard?