Usable Mantis is fork of Mantis based on 1.0.1 release code.
The main scope of the project is Making Mantis usable by wider audience, non-IT, non-technical users. As well as fixing many bugs and making other improvements along the way.
Usable Mantis is available for download at http://enargi.com

Of course forking is not so good and both projects would benefit if we merge our code into Mantis core and join Mantis project.
Problem is, among our improvements we added the Issue Type attribute to Mantis. We can't live without Issue Type and Mantis define all issues as just "Issue".  We needed adding Bug, Change Request,  Feature request, etc. issue types. We had to reuse "Priority" which wasn't used by our projects and rename it to "Issue Type" adding different values and such.
We could gladly join our UI changes and bugfixes with Mantis core, but Issue Type problem keeping us from it.

So our questions are:

Will Mantis have "Issue Type" attribute? And who decide that?

What is the standing on usability/UI improvements? Currently we are working on simplifying the issue list screen and making non-advanced Issue screens more simpler and readable. We also working on joining "Main" screen and "My view" into one. (Having both screens is kind of a waste and main menu exceed usability limit for number of menu items.)

What is the general plan for Mantis? There is no published Roadmap of Mantis beyond version 1.0.