This is a subject that is very close to my heart because I've spent a significant fraction of my professional life modelling binary systems with accretion discs in them. I would love to see interacting binaries in Elite - in fact, I think the inclusion of such common and attractive phenomena is extremely important for the explorer career. For example it is estimated that there are of order 100 million
cataclysmic variable stars in our Galaxy, so one system in every few thousand should contain one of these. That is a common enough object that they really should be included but still rare enough that they would be an exciting discovery - and just look at that image I linked to. Who wouldn't be excited to find one of those!
Regarding the difficulty of including them, I'm not entirely clear. As I said, I've spent a lot of time modelling these but with the aim of fitting scientific data. Getting something aesthetically pleasing is something I know nothing about

What I can say is that geometrically the accretion disc is quite a simple object. In the thin disc approximation it is simply that - a thin disc with a slight flare to it, like two round dinner plates stuck back to back. So the geometry is fairly straightforward. Texturing shouldn't be too difficult - these are discs of hydrogen, so they won't look too dissimilar to the star textures already in game. They are very hot in the centre and cool as you move to the edges, so you basically would want a gradient version of the existing star temperatures, transitioning from something hot and blue in the middle to a cooler star texture around the edge. It will have a sort of corona, which is already implemented for stars, and will be a bit wispy around the edges rather than ending abruptly: again, the diffuse edges of the current stars in game would do the job. So a bit of fiddling with what is basically already in game would get you a very reasonable accretion disc that would suit most people. Astronomers might start pushing for more detailed modelling, like ellipticity and spiral structure, but we're in the minority
There is also the gas stream travelling from the donor star to the disc. Again, existing textures in game could be reused: you basically want a thin, curved ray which is diffuse and corona-like.
The other component is the donor star itself. Now, this is tidally distorted by the primary star and so is slightly tear drop shaped. This
should have already been implemented: the i Bootes contact binary stars should both be teardrop shaped and touching, to produce a sort of dumbell shape. The first thing I did in every beta was to travel to that binary to see if they were correctly modelled and they never were: they were always two touching (or in some betas, slightly separated) spheres, which is very jarring to anyone who believes in the existence of gravity

I actually have a ticket in on this - it still wasn't fixed in 3.9, and I'm too far away in gamma to check. I'm guessing not yet. The geometry of this teardrop is fairly straightforward and was all worked out by the French astronomer Edouard Roche. he was actually namechecked in the newsletter which talked about the contact binary, which gives me hope that this issue is at least on Frontier's radar and they will get to it in time. Michael also said at one point with reference to the moons of Mars that 'asteroidal bodies aren't in
yet', or something similar, which also gives me hope that we will see more variety in the shapes of large bodies than the current spheres / spheroids we currently have.
So in summary, close interacting binaries would be a lovely addition to the Elite Galaxy. The geometry is trivial. The texturing is probably more complicated, but no more complicated than what they have already for stars.