Is that something that could be added via a firmware update?
Probably, but I wouldn't count on it. Canon has bigger fish to fry at this point. Linking spot metering to AF points is probably one of their top choices for "things to reserve for the more expensive camera", if they are indeed "forced" to start delivering a ~$2K FF MILC with both IBIS and dual SD slots. Gotta differentiate the lines somehow!
Of course, I could be totally wrong, and I'd love to see Canon have a corporate change-of-heart and all of a sudden start going gangbusters with cramming features into more affordable cameras.
I will say this, though- with the EVF, you've got both WYSIWYG and live histograms, so when shooting in manual exposure, spot metering linked to an AF point isn't really a must-have feature. You just dial in your exposure and go. Or if you're shooting in Av or TV, and want to meter off a face, you can just use Evaluative, since it does follow the focus point and maybe also take faces into account, (a little bit of "secret recipe" is always in these types of metering modes, Nikon's "Matrix" is even more mysterious WRT faces) ...and then just set the "command ring" on the lens to dial in EV comp as needed...
