If they should have had more armor parts they would also need to change the way enchantments works. if they had 6 pieces of armor instead of 4 the current enchantments would very quickly become overpowered. I wouldn't mind to see there being more armor slots it would allow for more variety when putting on armor. And more customization isn't wrong.

Not an huge problem, enchantment are linked to equipment type, however this let you get one more enchantment.
Downside is far less variation, gloves and boots you don't notice much unless they are totally out of place.
Say you have 8 outfits, that is 8 combinations, however with top and bottoms you get 8*8 variations, yes some of this will be stupid, so say 8*4 who is four times the numbers.
Only upside is that you don't get clipping issues between top and bottom, this was the reason most armors in Oblivion was the short jacket style. However it's no problem having both. You still has plenty of armor clipping in Skyrim, lots of gauntels dont macth all armor and none match robes, dresses clips with any boots is another.