I really don't have the same problem with resistances that Mr. Mearls does. I think giving out the occasional resistance is perfectly fine. The bigger problem is when these resistances are imbalanced, such as 4E's previously mentioned widespread poison immunities. Ideally, each element should have about as many monsters with vulnerability as there are monsters with resistance, and every element should have about as many as any other. In this situation, resistance only becomes a problem if you are playing an elemental specialist and are stuck fighting an enemy resistant to your chosen element, but this can be solved by removal of total immunity and special perks (such as Paragon Paths) designed to bypass such limitations.
As for the terrain "issue"... I don't think that is a problem at all. An ice wizard from the frozen north may not be skilled at fighting ice creatures, but often such a character shouldn't need to. Such a character, like the White Witch from the Chronicles of Narnia, is almost always portrayed as someone who either commands the creatures of that element and terrain, or serves someone else who does, not as someone who fights against the creatures of that terrain. Mastering ice magic amidst cold terrain implies that you are in harmony with that terrain, not fighting against it. This calls for the addition of special abilities and powers to an elemental specialist Paragon Path that let them work well alongside creatures of the same element, and certainly doesn't call for a change to the resistance system.
I certainly can understand criticism of 4E's use of elements (mostly because of widespread poison immunity and severe lack of vulnerabilities other than the undead weakness to radiant damage), but I don't think Mr. Mearls is chasing the right target.
As a side-note, my favorite system of elements is the one seen in the Fire Emblem series of videogames, since it tries the most to actually make every element well balanced. The three main "anima" elements are Fire, Wind, and Lightning, with Fire being effective against Wind, Wind against Lightning, and Lightning against Fire. Fire is effective against all beasts, Wind is effective against anything with feathered wings, and Lightning is effective against dragons. Everything has a consistent effectiveness against enemy types that appear fairly often (ideally), and they never deal with resistance at all, actually (other than the global resistance stats that serves as a defense against all kinds of magic, of course).