I realize that playing the Steam version of ESO means a reduction in income for Zenimax. But it also means that the players who are already members of an active Steam community will be happier (and more likely to get other members of that community to join) if allowed to get Steam keys. Playing a Steam game is a different experience than an add-in game, even if both utilize an outside launcher.
That being said. It clearly states on the Steam ESO page, that an ESO account is required to play. Why not make the use our existing accounts an optional purchase through steam for a reasonable fee? Say something in the $15 range? This seems to be a reasonable compromise to me.
What say you Zenimax? What would be fair for you as well as your users who WANT this option. Make us an offer.