WotC doesn't owe us support for anything. They can elect not to produce anything for any setting.
However, it would be in their best interest to maintain their IP by providing support for Blackmoor, Dark Sun, Krynn, FR, GH, Eberron, Mystara, Planescape, Ravenloft, Spelljammer, and Gamma World.
Personally, I believe they should have edition agnostic support for all of these settings up that establish personalities, timelines, plotlines, maps, etc... They should be out there with free access for players, and a DM access that is cheap - with the cost just enough to cover the cost to support the resources - that grants access that would not be common knowledge to players.
Then, they could still release 'crunch'/mechanics books that have classes, races, monsters, feats, spells, etc... and adventure paths at a cost. Those books would best be released in two stages: 1.) A very basic pamphlet of unofficial mechanics at the release of a new edition (like a UA article), and 2.) More robust books when they can be worked into the full development cycle.
You'd be ready to run any game at any point in the timeline in any of their worlds... but still be looking forward to the official setting materials.