IMO/IME those wanting more power from a WA are really only needing to do so if gigging with a small, single cab and probably no PA.
Those going for a two-cab setup with WA DI'd into another amp or whatever, consider that it's easier to make the 2nd amp and cab a ... WalkAbout.
Either WA combo with WA extension cab, or two WA combos ... or two WA combos with two WA extension cabs.
P-Nut with 311 (or some similar band of the era) had a gorgeous live setup of two wine-colored WA 12" combo and extension stacks, the pic of which has been posted many times, and Sigur Ros had what looked like dual WA 15" combos (or 15" combo & extension) - [This invalid link has been removed] - though I expect that'd get far too big on the low end at significant volumes sans-HPF, but for what's essentially stage monitoring a non-metal band you wouldn't need to turn that rig up anywhere near the point of it getting flubby.
WA combo with a powered extension speaker would also cut down on bringing the 2nd amp, or heck two WA in a rack would be about 28 lbs and run each one into a 4 Ohm cab.
Speaking of WA's with two cabs, anyone remember this?
Mesa Walkabout + TL806 special Retro look ...