It is not our plan to have "all the Openmark capabilities incorporated into Moodle". There will always be capabilities that other systems have that are prohibitively expensive to (re-)implement in Moodle. In OpenMark it is the ability to write arbitrary Java code to process the student't response and determine the feedback. In Stack it is that they have incorporated a computer algebra system (Maxima) written in Lisp. Therefore, the the current approach of using the Opaque bridge (Development:Opaque) to allow questions implemented in other compatible systems to be used in a Moodle quiz will continue to be a good option to have.
However, there are other times when it does make sense to re-implement certain functionality directly in Moodle, because a lot of people will find it useful, so it is worth making it available right there, nicely integrated with all the question editing and import/export that Moodle provides.
Free text matching is one of those things. I posted a few months ago about the OU's development roadmap for the quiz, and you will see that this feature is there. In fact, we have moved away from IAT, not because it wasn't working, but because we found that a simpler approach (The_OU_PMatch_algorithm) worked just as well and was easier to author questions with. So that is the way we are going.
This might be an opportune moment to announce that we are outsourcing the development of all those new question types, and the person we have contracted to do the work is Jamie Pratt. Jamie did the new quiz reports in Moodle 2.0 (again with the OU paying) and he made the Question creation activity module (it's downloadable from the modules and plugins database), and did a lot of work on the question bank at the same time. We will be publishing all these question types in the modules and pugins database once they are done, and there is a finished Moodle 2.1 that they can be used with.