I say - get rid of them.
I'm all for keeping the iconic Superman costume intact, but the undies have become a huge (pardon the pun) bone of contention. There simply isn't a
reason for them. The cape adds some regality, the 'S' is there for representing his family shield (or just signifying the word
Superman), the rest of the suit could be construed as a Kryptonian costume, etc .......... but the undies just are.
And as time goes on, and audiences expect more realism from their films, and Superhero costumes & effects get much more advanced, the red trunks unfortunately start to look a bit silly.
I've never felt that the costume wouldn't be the same without the trunks. Take away his cape, it changes Superman's whole look. Same for the 'S'. But the trunks are only a small part of it and in any pictures I've seen of him
without the trunks, I've never looked at it and thought "that's not Superman"'.
As long as you have something red coloured around the crotch region - to replace that part which your brain is expecting to see - then I don't see why we can't lose the trunks. I felt this recent photoshop (which is all over the costume thread) did the best job I've seen yet of portraying a Superman outfit without the trunks. But whether you look at it up close or from a distance, that is
still the Superman outfit - it doesn't detract from the overall look or make it look silly. It's 100% recognisable.
If anything, the outfit below without the trunks actually looks more like a proper Kryptonian outfit of some kind rather than a mish-mash of red and blue which Clark or Martha Kent threw together for him to wear.