Does anybody know if there will be a Neon Genesis Evangelion Platinum
Collection Boxset available at some point?

Not to sure about platinum but they do have the complete box set.

Neon Genesis Evangelion - Perfect Collection Box Set (8 Discs)

From the opening to the final Genesis; the complete Evangelion
adventure! Neon Genesis Evangelion is the story of a reculant young
hero, called upon to pilot an immense robotic weapon in battle against
alien invaders in the year 2015.


This limited edition in unique packaging contains all 26 episodes and
includes the Directors' Cut episodes. These were not just a remaster,
but a revised and re-edited special edition produced under the careful
supervision of its creators. This is the only version of the EVA
Perfect Collection outside of Japan to include the directors' cut
episodes, making it a must have for fans and newcomers alike.


http://www.play.com/play247.asp?page=title&r=R2&title=188772

From the looks of the adv website there is no current plans for a box
set. That dosent mean that they wont come out with one latter thou.

http://www.advfilms.com/CatalogFilms_Volumes.asp?Cat=12326&Title=Neon%20Genesis%20Evangelion%20Platinum