You are using '14 NEC in Tn already??
If you were here in NJ, and extending an existing circuit, it would be no problem, as it would fall under our Rehab Code in the NJ Uniform Construction Code.
Its the place I work at, even if the state hasn't adopted the new NEC, the practice in my place is use the most current one.
I was just curious if others have ran into this yet. I can see getting away with using mwbc for an existing'relocate' receptacle, but if you are extending to a 'new' receptacle it may be an issue.