I am going to keep this short, since I feel the argument is a simple one. Now that there is an official policy on Proxys for foil only cards like Kess in Legacy and Nexus in standard, I believe it is time for Wizards to extend the policy further to include CE/IE cards in the Eternal Formats.
I have no idea if this somehow infringes on the reserved list (not sure how it would...) but the merits of this have to outweigh the negatives. Access to cheaper duals for legacy, and additional power for Vintage players. This would add approximately 14,000 copies of these cards into the pool of available duals and power, and could help facilitate additional sanctioned Eternal events in the future.