The problem is that WotC doesn't like easily accessible two-color lands that are anywhere near the power level of duals. It takes away too much design space for the Standard they'd be in because they'd have to look really hard at the power levels of what got printed alongside those lands. Then they'd have the problem that people would talk about that Standard for years and compare following Standards in ways that were not complimentary and high-growth sales producing.
The solution is simple. WotC should print some limited edition dual lands with beautiful artwork and offer them only as trade-ins for existing duals with the understanding that they were going to print Modern Masters duals with less beautiful artwork shortly thereafter, in effect removing dual lands from the reserved list in the process.
Collectors get the choice of keeping their black-bordered alphas and betas, the rest of us trade in our white-bordered unlimited and revised for the "you can only get them this way foils (or whatever)" and both Modern and Legacy get an influx of real duals in the process. The price of duals goes down, with the exception of alpha, beta and presumably the traded-in-for foils (or whatever) and both eternal formats gain a major influx of players.
The Modern Masters with the new duals is the best selling Magic set of all time and it never touches Standard at all, preserving the "purity" and design space of the environment. The stores get to both trade-in their existing duals for presumably equally lucrative limited editions preserving their value in the deal and also sell Modern Masters.
Win for WotC, win for the stores, win for collectors and players for the most part, huge wins for Modern and Legacy.

