Mixing acoustic and electric guitars in 5.1

"Whatever sounds good and serves the music" etc etc...

The pop technique is perfectly valid and probably the best starting point, especially with rhythmic acoustics. Double tracked, hard-ish panned left and right. I often use the Ghz Panpot tool which does panning with level, frequency, phase and delay in varying combinations and give the impression of width without being absolutely hard panned. I'd avoid hard panning anything that doesn't have a friend who can live in the opposite speaker to retain that L/R balance, much like in a pop mix.

Something to bear in mind is that theatrical 5.1 has to cover a large audience space, so you'll have as many people sitting around the perimeter near to the surrounds as you do in the middle sweet spot. For that reason I tend to avoid putting anything that'll pull focus off to the sides/rear with rhythm, dryness or brightness, and that often encompasses guitars and other plucked stuff.

Also bear in mind that cinema installations often apply a small delay to the rears/sides (much like aligning a PA system), in order that people in the cheap seats don't perceive the surrounds as arriving before the front speakers. That can upset rhythmic perception if you do decide to put those elements hard in the surrounds.

You could absolutely quadruple track and pan all around, but probably more effective with ambient guitars or some nice floaty charango/mandolin arpeggios than hard strummed acoustics.

Reverb/delay etc of course also effective for getting full room coverage with guitars, but don't make it sounds substantially wetter than you'd accept on a stereo mix. To that end, always spend time monitoring the stereo folddown as well and make sure there are no odd phase cancellations going on and that you're happy with the basic musical balance.