what is an organelle is an interesting question…
it’s an equal mix of custom hardware, custom software, and open source software, that together make a musical instrument.
for sure that ‘mix’ is not tethered to any hardware, only the implementation.
this yields the answer to some of your other questions…
some of the code is based on the hardware that is present, specifically to get data from the keys, knobs, encoders and to write to the display.
if you have coding skill these could be replaced with any number of solutions…
but to retain compatibility with an organelle (so be able to use organelle patches ‘unchanged’) it needs to be done quite carefully.
a good example of what necessary is to think about the display/menu system used to launch patches, and also within the patch itself - how would you replicate this?
of course, you could just take PureData as you abstraction level (in a similar way to mother.pd desktop does), but this only gives a certain level of compatibility e.g. desktop mother basically doesn’t work at all for the newer graphical patches, or multi level menu patches. (and certainly not orac 
)
Im not saying its impossible, far from it, I’ve done exactly this kind of ‘emulation’ before… if you look at my Norns emulation, you’ll see its a similar concept
on my Norns emulation project, what i did was rewrote the entire UI from norns to instead use a push2 controller, and ran the whole thing on a rPI with PiSound, its done in such a way that its 100% compatible with the Norns, even down to scaling the display, and emulating add-on components like the monome grid.
(I could easily do exactly the same for Organelle, but im not going to )
so that brings us back to ‘what is an organelle?’
sure you can think of it as something like a rPI with a lcd display, keyboard, knobs, encoders and sound card added… but what this does not account for is the software that’s needed to turn this ‘generic computer’ into a musical instrument, where the pieces are integrated into a whole.
… this is why quite a few had talked about doing it, but few have actually done it
it’s no surprise that a computer can be a synthesizer (etc), but that doesn’t make it musical instrument, adding the physical interface, control, user experience does that…
but there is absolutely nothing stopping you doing this, and i’ll admit freely, its actually a fun thing to do - if you have the time and technical skills to do it.
to end on some help as to where to start:
use a rPI3 + PiSound, its imperative you have a good sound card. the standard rPI audio is dreadful.
(reddit post is wrong - bbb/bela is not suitable due to performance)
if you’re into diy electronics you can easily add pots/lcd display - but take care as the PiSound uses many gpio ports, do you might have to multiplex stuff.
if your not into DIY, then you could use midi, and perhaps a touchscreen?
or you might even take a shortcut and use something like http://zynthian.org
all approaches are going to end up quite a bit chunkier than an organelle, esp. by the time you add a keyboard, but that tends to be the nature of DIY (unless your getting custom pcbs/enclosures made)
from there you will have to alter/re-write the (C++) code of the ‘Organelle_UI’ which you’ll find in GitHub, and also adapt the various linux scripts to match your distribution.
anyway, depending on your skill set, it could range from ‘reasonably simple, but a bit time-consuming’ , to quite an ambitious (but fun) project.
