Would you watch part 5 if he did not have his iconic outfit in it?

yes I would.

I'd not even want a 5th movie at this point since it would just be Indiana Jones being too old for things and sending his son or someone else on an expedition to retrieve an artifact. He'd just be a supporting role and his son would be calling him every now and then to give him advice on what to do next.

id be fine people need to stop keeping these franchises in Boxes and Mangold has better Track this era than Spiielberg who hasn't made a good film since Lincoln

im not watching it, anyway

I'm a retired archaeologist. The Indiana Jones look was influential in the real world, because on many field projects some newbie would show up in a carefully beat-up fedora, and a shirt with the sleeves rolled up and the buttons undone down to his sternum. It got to be a real eye-roller.