Sorry I haven't spent much time on D2PK, so I'm not exactly sure.
But any items that are not already a part of D2PK probably weren't added for a reason.
I could be wrong, there could be a thing or two missing, or maybe you just couldn't find it.
But there is always the chance it was an item that was forgotten, and if so maybe it could be added.
As for what else you said, I don't think anything should really be paid for on the D2PK side of things.
It's meant to be a place to Duel against others with no advantage for any player in any way.
But if these items you speak of that are missing are truly one's worthy of being added to D2PK.
I'm sure someone who know's a bit more about D2PK will see your post and agree.
And hopefully soon answer your questions better than I am able to.