(cross posting with the WotC boards)
I really can't entirely agree with Mr. Mearls on this.
High level play hasn't seen as much attention because it can get funky and the rules have broken down. Even 4e grew a little softer in Paragon and Epic, with option bloat and poor math initially. And once the math was fixed Epic saw very little support. The problem is not that no one plays Epic or wants to play Epic, it's that we're not given the tools to make Epic fun.
"Tools" does not just mean mechanics (but does include mechanics) but also involves advice, adventures, advice, monsters, and maybe some advice. DMs need to really be aided and assisted in making high level play engaging and fun.
Similarly, Epic cannot be more of the same only with bigger numbers (like 4e). It needs to play and feel different. You cannot just "fight more powerful creatures and maybe visit a different plane". That could be handled by reflavouring. "This orc is really a balor". You may still be in a dungeon but it shouldn't be a plain old dungeon. Just because the dungeon is somewhere crazy doesn't make the experience any more grand and epic. High level play should embrace frequent teleporting, regular flying, and the ability to commonly do fantastic things.
Some of the article reads too much like a direct reaction to 4e Epic where hand size and option paralysis set in. Which is something to be aware of and avoided. But reigning in options too far just makes the game samey and limits the Epic feel. Epic wizards shouldn't only be Epic for two rounds each day.
There are plenty of examples of high level adventures, but most have been done poorly. I ran my group through the original Dragonlance adventure path, and had a lot of troubles with the last few parts. Mostly as the parties were becoming so high level while the adventures were not changing to accommodate the increasing power. The modules assumed people would go down with the sinking ship or spend weeks trekking across enemy occupied territory when the heroes were of a level when they'd have access to teleportation magic.
As an example of an alternative tactic, the next big Paizo release for GenCon 2013 is Mythic Adventures, which is the Epic rules for Pathfinder. Only instead of additional levels, it's a power boost that lays overtop the existing rules. This will probably work adequately at best with PF, but with 5e's designed modularity a similar tactic might not be a bad idea. For the people who want to play Big Damn Heroes from the start of the game.
The legacy system sounds like a good example of a rules modules that should be possible to overlay at any level. Likewise, there should be ways of making the low levels a little more heroic and epic.
For rituals, sometimes the simplest way is the easiest. Only change gold when the ritual has a level equal to your highest or second highest spell slot. This mirrors 4e where the cost of low level rituals was negligible without actually having to overly inflate the cost of rituals or ask the high level party to track minor amounts of gold.
At 5th level the wizard and cleric can just cast 1st level spells as rituals for free.
