(And first, no, a lack of response from him up till now didn't imply any subtexts... it just meant he was busy and/or checking with the class devs and I wasn't going to bug him again till I heard back!)
His response is this (paraphrased):
- Any retained features that are actual buffs are a definite no-no. Anything that affects class balance by buffing your pet is out.
- For anything that just affects cosmetics/appearance, you have to use your best judgement. If another player could conceivably get upset because it somehow affects gameplay - making it difficult to target, obscuring vision, (maybe looking like a worgen player?

Then again if you already had a pet removed because the cosmetic buff was causing issues that made players report it, and you went and did exactly the same thing again, I imagine you'd be treated with less sympathy

EDIT: also forgot to mention that Blizzard are working towards more stringent fixes for retained buffs, but I was given no time frame on that. Not sure if anyone is currently working on appearance-only ones.