First of all, thanks a bunch for udisks: with my Tails (https://tails.boum.org/) developer hat on, I can say that the LUKS integration within the desktop, that udisks allowed, has been a huge step towards making it possible for non-technical user to protect some aspects of their privacy. Some of the custom Tails applications also rely heavily on the udisks D-Bus interface.
Now, LUKS is not very well supported cross-platform, that's why a number of our users are still using TrueCrypt volumes. This is a pain to support for us, and we could not see the light until recently, cryptsetup 1.6 added support for the TrueCrypt on-disk format, as documented in the "TCRYPT (TrueCrypt-compatible) EXTENSION" section of cryptsetup(8).
So, on this side, we're back to the good old days: advanced users can do their stuff on the command-line, while less tech-savvy ones are left behind, using less-free software solutions that, for some, may put them in danger in the field. That is why it would be great if support for this TCRYPT extension was added to udisks (and then to GNOME Disks, etc., but one thing at a time).
I'll try to find someone who is able to contribute a patch, but I'm not convinced this will work out well, so if someone who is comfortable with the codebase already is happy to do yet another bit for privacy, there you go :)
Thanks for your attention.
this ticket was not addressed in over two years. I want to note that this is still an open issue. Even though TrueCrypt development was discontinued in 2014, TrueCrypt-like volumes are still the most widely used solution for cross platform encryption. The TrueCrypt fork Veracrypt seems to be the predominant successor, with support of VeraCrypt volumes added to cryptsetup in 1.6.7 . And still many Tails users ask for a GUI for TrueCrypt/VeraCrypt volumes.
If no one who already knows the codebase is willing to work on this, I plan to prepare a patch myself at some time (which might be in a few months). Before I do that, I would be glad about comments about the general willingness to include this feature.