The reason Morrowind had more diversity was because of its graphics. Devs could get away with the diversity because most of the armors lacked any 3D-definition. Sure, there were bumps and such on armors to signify that some pieces weren't just blocks, but the time it would take to individually sculpt pieces of armor to great detail would be tedious.
I'm not following the comparison. True, Oblivion's armor as compared to Morrowind's armor had a bit more 3D definition, but Oblivion's armor still used normal maps like crazy, just like virtually everything in Oblivion. If it's a concern that their current team can't manage a bit of 3D definition coupled with mixing and matching while avoiding clipping, then see below.
What Bethesda did with Oblivion was make things more efficient. Why wear pants underneath chainmail greaves? you wouldn't even see them.
"Efficient" in terms of in-game options is only good when the complexity is something that almost all of the fanbase uniformly despised. And I think it's incredibly safe to say that the fans of armor-over-clothing and mixing-and-matching render that a nonissue. Why wear pants underneath chainmail greaves? Why not? Why not wear robes over armor? Why not wear only one guantlet just to look cool? Why not do any of those things? That to the clothing/armor world would be like saying, "You don't need all of these guild options" to the faction world (Oh, and whether the pants could be seen or not under the chainmail depends on how the chainmail greaves were designed relative to the pants).
Besides, any "resources" argument is pretty null and void by the fact that their team has significantly grown in size from Morrowind and Oblivion. They, with their current increases in employment, can handle creating mix-and-match pieces and clothing-under-armor. And anyway, so long as they laid out mesh-design (and body-part replace) rules and stuck to them, they could avoid clipping entirely as opposed to going back and fixing it after the fact.
As for pauldrons, most are generally attached to the armor in the first place. There are some pauldrons that don't require the chest piece, but allowing pauldrons to be seperate, just for the sake of a few exceptions, would be annoying.
In your opinion. I find that pretty much everyone else on these boards would welcome the return of interchangeable pauldrons, and they don't care in the slightest if it somewhat unrealistic from earthly armor designs. This is TES. It's their party, and they can design armor types with separate pauldrons if they want to.