I disagree. The portrait could just as well be their to commemorate his long time service as mayor to the town. There are so many other possibilities regarding why Tortimer is no longer mayor. To me it just seems so un-nintendo like to kill of an old turtle that has been their since the very beginning of animal crossing, and not to mention extremely uncreative.
For instance, perhaps now he is travelling the world on the train, stopping here and there to drop of special event items, or maybe living on the island, in the town, or even as a new neighbour .
All these ideas just seem a little more colourful than killing him off, or having him excluded from the game altogether (minus the picture).
Still going to be an awesome game though : D
YEAH I AGREE WITH THE FACT NINTENDO WOULDN'T KILL HIM OFF (whoops didn't know caps was on and i cbf typing it again so i'll leave it, sorry)
Berry said the portrait could be a type of 'Easter Egg' I kinda agree but they're suppose to be more or less hidden.
I think he'll get a mention near the start of the game, and we'll find out then why the portrait's there.