Design a TARDIS console room

It's quite pretty actually, Mark Gatiss does an excellent job making it sound otherworldly. It turns up in Nightshade and might be one of my favourites.

The theory certainly has legs. The Seventh Doctor might have the longest life out of all his incarnations, barring his immediate successor.

That's certainly one interpretation. It's a story similar to say... The Cabinet of Light or The Dalek Factor. It deliberately obfuscates its own timestream, but goes out of its way to dismiss the concept of it being in a parallel universe. There's something else going on. The incarnation here could very well be a young First Doctor, a future Doctor who has retired to Gallifrey (maybe the same one in The Massacre novelisation?) or a completely alternate portrayal living in a universe where his past history was retroactively altered like what happened in Blood Heat. When an examination is made of other timelines, they're said explicitly to be palimpsest, not parallel. Their/our universe is riddled with paradoxes, which could quite possibly be the result of the Faction or the Doctor's own cavalier adventures.

Oof, well... TARDISes have the capacity for telepathic speech, not all Time Lords are Gallifreyans, the Magistrate is implied to be a beneficent Master (which squares with The Adventuress of Henrietta Street), Seeing I is mentioned, Attack of the Cybermen gets a look-in as the basis for a hypothetical scenario, the Sontarans and the Rutans make peace after centuries of war, the Doctor meets Patience who has distinctly experienced the events of Cold Fusion, he's said to be less than two thousand years old and has travelled widely. Throw in the physical description and I'm very inclined to believe it's the Eighth Doctor towards the end of his life or at the very least an incarnation "played" by Paul McGann.

Gabriel and Tanith in Falls the Shadow emerged from the anguish of every timeline negated by the presence of time travellers, so it's possible that the Doctor's restoration of Gallifrey had other consequences beyond the purely spatial. If the fabric of spacetime knitted itself back together again in lieu of the Time Lords, then it might have been necessary to rip it back open again to place everything back as it once was. Not a reset, but a suture and its still fresh enough you can see the scarring.

Ooh, possibly, but the book tries to fight that particular definition as well. It's "canonical" in the sense that the television series is and the Unbound stories aren't, but Omega is deliberately altering the past to suit his own affairs, so it's very difficult to say. The Doctor experiences multiple pasts, including those he knows never happened to him.

Having read The Cabinet of Light, I was kind of amazed by how much the new incarnation who employs Honore Lechasseur sounds like the REG Doctor (he's pale, has a high forehead, smokes and has a marvellous singing voice). It predates Scream of the Shalka only by a matter of months. The Dalek Factor is a little trickier, there's only reference to a companion who met a very unpleasant end before the book starts and the book ends with the Doctor reconditioned and forced back to the start. Again, again and again, until the Daleks get it right. It could very well be something to do with that incarnation, the Eighth Doctor or it could be his very last story and he never escapes the Daleks.

Didn't it really? Sourced from the eBook version that once existed on the BBC website, the passage describing the room in question was:
It's a beautifully sad book really. Nightshade is all about nostalgia, regret and a deliberate reaction against the garishness of the eighties. It starts with a depiction of the First Doctor's departure from Gallifrey (most notably, alone) and the First Doctor's decision to retire and ends with him betraying Ace and abducting her for the greater good. Very raw and well worth the read, even with the audio adaptation.

It's certainly not out-of-character for the Eighth Doctor. I'd have a harder time believing with someone like the Fifth, who probably enjoys the stability of one room, but his eighth self might do it just for the sake of variety.

It's certainly possible, although it may not be the same console anymore in that control room.