I don't know if a thread about this exists somewhere in the vaults, but supposing the Eon/McClory business hadn't happened or had been settled without the prohibition preventing the official series from using Blofeld and SPECTRE? I only wonder because of course SPECTRE has become the flavour of the month in Bond villainy, right down to the new film's title.
Which films post DAF might have used SPECTRE or referenced it? My own thoughts below.
LALD - unlikely, coming straight after Blofeld's presumed demise in DAF. But, in the book Mr Big worked for a larger organisation, Smersh, so who knows?
TMWTGG - again, unlikely, though SPECTRE could have been referenced as having hired Scaramanga in the past.
TSWLM - if SPECTRE had been available the film might have been different, from what I've read over the years. But even if the basic plot had been the same, I could picture this as being Blofeld's comeback movie. Whether this master criminal would have been interested in creating an undersea civilisation, rather than the usual blackmail routine is debatable.
MR - too soon after TSWLM, and I don't think creating a new "master race" would have interested ESB.
FYEO - well, he was in the PTC but nobody mentioned his name - like Basil Fawlty trying not to mention the war in Fawlty Towers. But this film is often compared with FRWL in plot. Might we have seen SPECTRE agent Kristatos attempting to obtain the ATAC for Number 1 to sell to the Soviets? And Bond barking up the wrong tree for a while, thinking "The Dove" was really working for The Octopus? Speaking of which;
OP - adding Blofeld's organisation to this film would have complicated an already complicated plot. I think this would have stayed pretty much the same.
NSNA - would this have been made? Possibly, if only for an alternative take on Bond and Blofeld.
AVTAK - as with OP, I don't think this would have leant itself to a SPECTRE association. Zorin was the 1980s answer to Goldfinger in his plans. Russian links aside - which he broke anyway - Zorin was his own boss, and I don't see this as a Bond-v-SPECTRE movie.
TLD - I have the same view on this as OP - strictly a spy-v-spy Cold War movie and adding another layer of villainy would have over egged the pudding. That said, Brad Whitaker was set up in business through "various criminal organisations". SPECTRE could have been referenced in passing.
LTK - I read somewhere that the script at one point included an appearance by General Pushkin. To what end I don't know. I see this as a personal revenge movie in which the bad guy happens to be a Latin American drug lord. I think it would have stayed the same.
GE - after a six year hiatus - suppose SPECTRE had apparently vanished, and Blofeld really had died - but then the organisation suddenly reformed in post Cold War Russia? And was headed now by a former Double-0 agent? Just a thought.
TND - pretty much as the finished film.
TWINE - as with OP and TLD, would have overcomplicated things.
DAD - strictly Bond versus N. Korean bad guys. Again I don't think that organisation would have played a part.
CR/QoS - Quantum would have been unnecessary.
SF - I think Silva was a lone operator with a personal agenda. SPECTRE could have been referenced but not included as part of the plot.
In the series up to 2002, I think we might have seen the last of SPECTRE in GE, unless the films following were somewhat different from what actually was produced.
Well, those are my thoughts.