A friend of mine had (what I consider to be) a phenomenal idea about a hypothetical Blofeld cat during a discussion about Skyfall's Komodo dragons.
Blofeld's interests could include the raising and/or possession of deadly or endangered animals (along the lines of his otherwise-pointless-except-for-killing-underlings piranha pool in YOLT). Could be any number of character-based reasons. Maybe he likes the reminder of death always being near. Maybe it's a precursor to a Garden of Death itself - he has an environmentalist/preservationist bent as an outward guise but doesn't limit his "collecting" to poisonous plants. It also includes lethal species.
So, the cat? It would be a small/baby white bengal tiger that he's tamed. It would still be occasionally nasty. Not exactly a lap animal all the time.
http://en.wikipedia....iki/White_tiger
Maybe one of several. Maybe he "resets" with a new cat/tiger every few months. And at some point, he'd get to deliver a wonderful Silva-esque monologue reflecting the inevitability of time/survival in a harsh, unforgiving world as the animal matures, changes, and its natural instincts take over. Probably in some situation where he's trying to recruit Bond for SPECTRE.
"My friendly companion loves me. It needs me. And one day it won't. Its instincts will tell it that it's supposed to kill me. That's my reminder. That every thing in my life will inevitably decide my life is worth less than what it instinctively needs. We cannot attach ourselves to anything but ourselves. Our own survival is always paramount - caring about anyone or anything else is an opportunity of convenience, at best. Your walls will fail you too, Mr. Bond. A country, an institution - they will outgrow you long before you outgrow them. Ideology is no different. That is why we operate without one. And that's why your place - the only place you could ever really survive - is with SPECTRE."
Bond would then issue a simple rejection phrased around this all being about Blofeld's inability to keep said pussy satisfied.
How about this - Waltz character really is Franz Oberhauser, throughout the film we see him sitting at the top of the table in a conference room with members of SPECTRE - at the end of the film Bond breaks into the room to see the room empty, apart from the cat walking on the table towards him. The cat looks up at him and says "I've been expecting you, Mr. Bond. My name is Blofeld" - role credits!
Failing the above, I'd also kind of love this.