There is of course an assumption that for harvest festival we would be growing vegetables for cooking on the 26th, but if it was similar to new leaf it could be a combination of foraging and speaking to villagers.
I must admit, I have not much experience in New Leaf, and as I'm planning to play in the future, I don't really want to spoil myself. Whatever I "predict" is not solely based on NL whatsoever.
What I wanted to say, comparing to Halloween - we had more time than less than two weeks for Halloween preparation. This is a fact.
Of course I don't know what may happen in Thanksgiving Day, if anything will happen - because this day in the game may be just like any other days.
Just to play devils advocate a bit, new mechanics in the game so far have not been "dependant" on season events. So a new mechanic can be introduced separately from a seasonal event. No doubt for players who miss the actual date.
Sure, you may be right.
Planting and growing pumpkins are not tied to Halloween, dreamsuites, swimming, art, shrubs. So a cooking/vegetables mechanic does not have to be tied to harvest festival. It may be that simply on the day itself (26th) we use the new mechanic to help Franklin cook, but we collect the ingredients in the usual way.
I'm not sure, maybe I don't understand what you meant, bud if I did, I must disagree with you, and ask for more explanation. Why do you think "Planting and growing pumpkins are not tied to Halloween"? I can agree, after Halloween, whoever wanted, kept pumpkins and they probably will grow until the end of times ;-)
Then as part of the new mechanic, cooking, more ingredients are added. Those ingredients can be planting and grown same as pumpkins.
Sure... everything is achievable if developers will implemented in the game.
This is all speculation based on datamines, though if cooking is added as a mechanic, I'd look back to swimming and diving and art collecting as a kinda of what's the point to it....it would make sense to have some kind of purpose to cooking or reward system. With redd you fill art in the musuem, same with diving, so maybe there will be somewhere cooking has a home for.....like a cafe......again speculation.
So... swimming + diving, I can call "daily activity", something what is a part of daily life. As addition, like a fishing - it's a source of goods, we can sell (but not trade), give to museum, and have some achievements for miles.
Art collecting - I can call "event" with higher rarity. It has multiple purposes, like filling museum gallery, making wrong decision and buying fake art, using those as an addition for decorating house / island, sale / trade, and finally achieve more miles.
Sure... those above serving as a purpose.
But we still have fruits - starting from just one, native fruit - and in time we can get all available and some may say, it serves no purpose, as mainly we just selling those fruits. I will not spoil everything, as whoever playing ACNH already seen the beginning... and one of our first missions was gather some fruits to prepare juice / drink, do you remember? So some "cooking" feature is already mentioned... however abandoned or not explored yet.
Quite often we may observe like villagers walking with drink (not canned) or sandwich. Of course it could come from wending machines (if placed) - this could be logical explanation, but many of villagers really like food. Cooking could be a really nice addition.
Of course cooking may not come at all, although Nintendo has shown a love for it a lot recently, breath of the wild, Pokémon both had pretty great cooking mechanics.
Let's hope we get something special.
As I never played any Pokémon games, I will not say anything, but BotW gives a really good cooking mechanics, but in there we rely on anything can be gathered and there's absolute lack of farming. I may agree it's sufficient as the world in this game is huge enough and we constantly have fresh supplies of almost any ingredients.