Personally, I find it very interesting what has bled into my own gaming play from the 3e+ era. They often surprise me, because rather than being big design ideas they are minutia that actually makes interacting with my world a little easier for my players. Languages were one of the first that I noticed.
Another is the non-use of electrum. Despite the fact that it is a naturally occurring metal (with a mixture of silver, gold and a variety of other ores) that was used in coinage in several parts of the ancient world, it messes up the wonderfully easy to understand decimal system of 3e+ coinage. So, despite the fact it exists in both older versions of D&D and its clones, and despite the fact that Gygax had it exactly correct that electrum is half-way between silver and gold, my players have rejected it out of hand as part of their game play.
My problem is that I have always had a soft spot for the metal. It is possibly more historically accurate as a type of coin than either gold or platinum. It conducts electricity. Its name sounds really cool. Yet, my players are absolutely correct that it is just a pain to include it in the game as half a gold piece.
I mention all of this because I ran across this hymn today while chasing down something I was researching:
Beholding the orders of the Angels in manifold form, Ezekiel proclaimed them in his history long ago; among them stood the six-winged Seraphim, and the many-eyed Cherubim compassing round about; and with them he saw the Archangels shining like electrum and glorifying Christ unto all the ages. [my emphasis]This got me thinking that I could re-introduce the metal into my game as a magical metal. Whereas adamantium and mithral are arcane metals, electrum could be a metal used to create/channel divine magic.
Unlike adamantium and mithral (which are ostensibly forged by a class that cannot use them in most applications), electrum could be fully taken advantage of by the spell casters who forge them — clerics.
Herein is another way that 3e+ design can sneak in to my game at a more fundamental level: rather than tying metamagic feats to players, I could tie them to various applications of electrum.