If no editor required, then it needs to be a simple amp. No effects, or just reverb. The minute you get into effects, you either need an app, or the effects control is heavily gimped. This is why I dislike the Katana, and all these other amps with built in effects.
With enough encoders on board, you could have it both ways. The most relevant parameters to adjust things to accomodate a given situation should be all exposed.
As an example:
- 2 x amp and boost: Amp type, gain, BMT, volume, boost gain, boost level. Anything beyond that could be covered either by secondary encoder functions or through an editor. 8 controls per channel in total.
- FX section with, say, delay and reverb. Time, feedback, mix for the delay, decay and mix for the reverb might already be sufficient as permanently exposed parameters. That's 5 more encoders. If one really wanted, there could be a modulation section, too, exposed parameters would be type, speed and mix.
- Master section. Ideally featuring a simple (possibly pre-adjustable) B/T master EQ and output volume.
That'd be 27 encoders in total. Yeah, seems like a lot, but in the end it'd still be way less than on any mediocre pedalboard.
And as the entire amp should be programmable as well, you could either use that programmability for, well, what it is (as with any programmable digital device) or just save a bunch of "2-channel-plus-boost-and-the-most-common-FX" WYSIWYG setups.
I would possibly be able to play almost all my gigs with just a handful of 2-channel layouts already.
Make all this super lightweight, so you could use a strap and carry it over your shoulder, on the train, on a bicycle luggage rack, whatever.
As said, I'd buy that in a hearbeat and pay decent money for it.