At the moment the elements which I feel need to be mechanically addressed are the various fantasy races, the classes which objectively exist in setting (e.g. in setting one may refer to Mazlan the Black as a wizard but could call both Kragor the Hillsman and Darrick the Swordsman warriors) and perhaps most importantly magic.
For the races I'm planning to use some of the ideas presented here to assemble ability packages for the default races presented in the Forgotten Realms Campaign setting.

In regards to classes most of them dont require any particular additional mechanics. After all the difference between a Barbarian, Fighter, Monk and Paladin are primarily flavour based and can easily be mirrored via Esoteric Disciplines and Martial Techniques.

The classes that perhaps need to be addressed mechanically are the magic using classes i.e. clerics, druids, wizards and sorcerers. The magic system presented in Reign is fairly different from the standard D&D one and if used wouldn’t produce the same "feel". After thinking about it for a while I thought that perhaps the best way to do it would be to use the power creation system from Wild Talents to mimic the traditional abilities of D&D magic users.

Perhaps through the use of a new Advantage where a magic using character would pay X character points to gain Y Wild Talent creation points. Such creation points must be used to purchase powers which fall within the general purview of the class e.g. wizards can’t have any healing effects while clerics can. I was also thinking of including three new skills Prayer (for Clerics and Druids), Thaumaturgy (for Wizards) and Sorcery (for Sorcerers) which are used when casting magic. Having magic use tied to a skill is appealing to me because then specialisations and clerics Domains can be represented by MD or ED (e.g. a Wizard who specialises in Necromancy rolls Stat+Thaumaturgy+1MD when using Necromantic effects but suffers a -2d or -3d penalty when using effects from an opposed school, Clerics gain +1MD when using a spell tied to any of their patrons domains but suffer a penalty when using opposed effects).

However, while I own Wild Talents I haven’t had a chance to read it yet and so I was hoping that those with some experience with both systems could point out any obvious flaws with the idea.

Also if anyone else has used Reign to run D&D or has any suggestions on how to do so or what should or should not be mechanically represented in order to generate the right "feel" feel free to chime in.