perhaps this has been done to death.
the power supply and cooling fan are there for a start.
Sees like a dumbing down, kill the brain and take the heart.'
But I do not want a guitar amp to sound too smart, just make the guitar sound like a louder guitar.  Most of the modern amps miss that point.

How small can you go with a guitar amp?
Put it into an Altoid box?
If you have an cell phone, that could work.
But if you want to get real and rock, you need to blast.
And to blast you need at least 1 x 12 speaker, or 2 x 10 to get the db level.
And if you play bass, you need to move more air, so more power to drive the chain.
If a guitar amp is a wart on a power supply, and my wife is the power supply, and she can sing as loud as Kate Smith, can I tap into that power supply?
You bet, but she will not let me get near her with my guitar.
Can we talk about the future of energy and how to make things more energy efficient?

The chip amp in my Altoid box may be the best in show.  Or how about
The Marshall stack with 8 speakers and 100 watts of vac tube power?
No contest.  One gives you a kiss, the other makes you deaf.
There is a time and place for both styles.
A bedroom amp can be your best friend, but if you play out and with a drummer or jam,then you need to get loud.  I like to bring a medium sized combo amp, at least 30 watts tube, or 65 watts transistor with a good 12" speaker.  And you must be able to crank it up, get a screaming feedback at earbleed volume, and be able to control that feedback from the instrument.  Then hit the pedal and take it up a bit higher.
Now you have something to work with.

What makes a musician select an amplifier to use in performance?
For me, it must have a pleasing tone, be easy to control, and work well with my guitars and my effects.  I select something with a good clean tone, lots of headroom and portability.
A combo style is nice for general use, and should be powerful enough to drive external speakers.  I started out with a Fender Super Reverb and a Tele.  I still love the Tele, but have gone thru many tube style amps.  Now I do not want to lug around any extra weight, and I want the most pure, clean and powerful bang for the buck.  So I am going with the solid state designs.  Most of the commercial amps have crap speakers and useless add on effects.
Just give me clean and clear, light weight and sparkle and sustain.
I have been picking up some nice 1 x 12 combos and doing modifications to get what I need.
Over the years I have built many tube amps, and love the tone, hate the cost of the retube.
I am loving the silicon sisters.  Big sound in small packages.

Or to find a way to continue playing electrified music as the cost of energy rises.
Battery power is an option, the newer designs require less energy.
In the future playing to smaller audience, perhaps back to crystal radios with tiny ear buds for the listener?
I just do not see a future for stadium rock.