the real question is "where is the switch?"
will they switch clothes depending on seasons or if they are inside/outside or will they take the temperature in mind no matter of season or indoor/outdoor.
i think it will be a temperature system from the dev comments so far, so they might also switch to winter clothes when entering a very cold house or summer clothes if someone is heating like a maniac. its unlikely but if the temperature is different for every room rather than the house as a whole they might even pick up a jacket when going to the cellar. also there could be some flaws with this that need to be handled seperatly so sims dont switch to summer clothing when they approach a fire in winter and stuff. maybe there is a body temperature that takes some time to adapt to the surrounding temperature so a almost dead freezing sims wont switch to lighter clothes the moment they go through a door, of course if heading outside they will pick clothing in advance. best would be if sims need to go to a corresponding item (wardrobe, dresser) to switch clothes and dont do it on the spot.
we have to see how they have handled it in the end.