So...what is the point in everyday wear now?

Based on the livestream it seems your sims will only change into their normal wear when going indoors if the temperature inside is warm or cool enough because it can be cold enough inside that your sims will put on their cold weather wear and vise versa if it's hot inside. That's what the thermostat is for, to help keep your sims warm or cool.

Now to my knowledge your sims can't die from the cold or heat when inside (unless you use the thermostat) but they will be very comfortable.