Well, this has come up many times during her face run. At the moment, a Mickie James heel turn would be great to give her something fresh to do & actually have something for the audience to care about concerning the Diva's division. She is going off crowd reactions from her past & her wrestling ability that will soon dwindle slowly as she remains a pretty face. She mas the ability to pull off anything & is much better suited to the heel role, but her in-ring work suggests her to be the face. Much like the same with Rob Van Dam when he entered through the alliance.
However, if Mickie were to change status... there wouldn't be anyone else to take her place who can achieve as great as success as Mickie. Kelly has the crowd reactions, the beauty & can make the people turn heads, but her wrestling skills aren't good enough for being a face. Beth Phoenix is the total package, but her gimmick would better suit her as a heel & another Phoenix/Mickie feud would not do too good these days. That leaves Gail Kim, who cannot get any crowd reactions & is still serving her time as being a TNA outcast in the WWE universe.
Mickie is the face of the division much like Cena. You can't switch her fan alignment though it would be nice to see & can be easily pulled off. Oh, and for those like Saritafan who have no idea about movesets that say Cena/Mickie only know four moves & pander to the crowd to get over... you might want to watch one of their matches one time to find out they know more than four. Cena has the AA, stf, five knuckle shuffle, leg drop, spin-out powerbomb (thats five), throw back (thats six), bulldog (thats seven) & the fisherman's suplex (thats eight)... these are the ones he uses regularly. Mickie has the DDT, spinning back kick, the Long Kiss Goodnight kick, neckbreaker, lou thesz press (thats five), flying forearm (thats six), Mickicanranna (thats seven), dropkick (thats eight)...
I could keep going, but this isn't the time for this. The bottom line is that a Mickie heel turn would benefit audience interest in the division, but not the division itself.