The red underwear would look out of place if they tried to bring it back now.
It's not underwear. It's a pair of trunks, like swimwear. It's the sort of thing that circus acrobats and strongmen in the 1930s wore over their tights for modesty.
True, but Superman hasn't looked like a circus acrobat or strongmen since, well.... George Reeves in the 50s.
If they were making a Superman movie set in that time period, I'd be all for that look (or even if it was a retro-styled movie like SR). But in a grittier "real world" Superman movie, I just don't think the trunks really work as well.
Just like Hugh Jackman would look decidedly
less badass if he were running around in Wolverine's blue trunks of the classic comics. Lol