Not saying it should be given any priority over the stuff you mentioned, but I am saying it's "missing" from a product like Axoloti. You said it yourself, Axoloti is designed to permit the creation of a standalone product. That means the Axoloti Patcher is essentially the "development facility" where the design of that standalone product happens!
I do agree about it not being a good idea for it to be an object, but that simply means I think it should be part of the Axoloti Patcher environment rather than part of an Axoloti Patch. Pointless it being part of a patch cause like you said, surplus to requirements once the product has been designed.
But it's the process of design I'm getting at so here are some examples. I might be designing a parametric EQ, and using functions to adjust curves, responses to knob sweeps - so I want to see what it's doing on the spectrum. I might want to use functions to create a custom filter - so I want to see if I'm getting the desired curve - I need to see the spectrum. I might want to design a drum synthesizer and compare various topologies at the bottom end through switching between them. Again, I need to see the spectrum!
They're just examples for wanting a spectrum analyser.
There's actually a few essentials missing from Axoloti at the moment if looking at it from an audio design perspective. There's the lack of the spectrum, there's no band-reject (band-eleiminate) filter, and there's no system in place to ensure that when a person adds a dial or control to an object, it auto-creates an inlet for it. Take that last one for example. People are attracted to Axoloti diue to the promise of being able to be standalone and connect your own controllers to it.
Fact is, you're doing no such thing unless you know how to hack the code of almost every object in the libraries. The prioblem is that when people add a knob or button to an object, they seem to forget that the button and knobs they are adding are gong to be inaccesible when the product goes standalone. So to remedy that, I reckon Johannes should modify the system slightly so that whenever someone codes an object with buttons or knobs, the Axoloti environment auto-adds an inlet for it so that people can actually use it standalone (cause that's what they're expecting from Axoloti).
So there's a few areas Axoloti is still in it's infancy, and by no means do I expect a spectrum analyser to get any sort of priority over the other stuff, but it is definitely missing cause Axoloti Patcher is an audio product design envinronment.
Of course I'll do as you all suggest, I'll continue to feed another program with the audio, but it's still "missing" and it's something I personally would love to see become part of the Axoloti Patcher some day (as part of the patcher, not the patch)