Honestly at this point I think Nimbly has great potential to be a second-stringer it's just a matter of deciding which utility you want her to have, which is a case of Choice Paralysis. Gmork just kinda hugely overshadows her Nasty Plot build by speed and power, and I'm usually reticent to build two pokemon too similar or they just end up serving the same purpose and treading on each other a lot. Especially when Nimbly has a lot of other options that are just as viable as a heavy duty special set.

Personally I'm still leaning toward either the Scope Lens Substitute (maybe with Payback?) build for the crits or just Choice Scarf her and run Dark Pulse|Aerial Ace|Sucker Punch|Heat Wave to deal with her low speed. What Nimbly brings to the table is distinctly more situational and more roundabout than Gmork but she can still make it work imho.

But again, this is just my perspective. All I can do is give you best educated guesses really, I'm no pokemon wizard.