Full page, keyed and unkeyed maps.
Full page, high resolution artwork of all the artwork used on the adventure.
More full page, panorama style pictures of everything the PC's would see, especially locations.
Adventures presented in the same format as there printed modules (KoTS, etc.), with monster stat blocks, traps, etc. presented at the same place in the adventure as the encounter, not all collected at the end of the adventure.
*Not required to win me over for a subscription - but adventure specific battlemats/tiles for each adventure would be a huge plus.
And I'll second the tokens. Tokens seemed to be a standard thing in the mags for a while. I don't know why the idea was discontinued, but it was an awesome idea. Even better would be original artwork and representations of monsters in the adventures, as they would look or be encountered in the adventure, presented on tokens, rather than just the standard MM pictures.
Even in the print magazines, they used to reprint the cover art on the inside of the mag, full page with no writing on it. Seems like since the product is now 100% digital, there should be absolutely no restriction to full page versions of all artwork.