No, there is no proof that Mystic Decree will be in Mirrodin. All I have are these hints: The notorious Randy Buehler, who knocked a mana off Fact or Fiction, prices a vanilla hard-counter at 1UU. This makes it fall in sync between the current soft counters (1U Mana Leak, 1U Flash Counter) and the current hard counters (2UU Rewind, 2UU Discombobulate). He had a poll and everything. He seemed pretty content that 1UU was correct. Maybe because FFL's been playing it that way for a year now. Mystic Decree is still a good counter. The lack of a vanilla hard counter, to me, is very inelegant in design. All the color's base mechanics need to work off a model card. I consider Stone Rain, Demistify, Holy Day, Giant Growth, Naturalize, Inspiration, Unsummon, and Shock to be model cards for mechanics of the color wheel. There is an anomaly when an environment hits a 'critical mass' of countermagic. R&D tries to avoid this, for example during Invasion-Odyssey-7th Type II, which is why Fervent Denial isn't 2UU, 4UU flashback. There was already too much good countermagic with Counterspell, Force Spike, Memory Lapse, Absorb, Undermine, Dromar's Charm... Whenever I see something suddenly nerfed, I think of it as paving the way for improvements later. This is why I think Invasion Tap-duals in 8th are fine, since we already have Ons fetchlands, but there might be another excellent set of dual lands in Mirrodin (policy says allied colored duals always are printed in the big expansion of each block to facilitate multicolor play). I thought it was obvious that Counterspell wouldn't make 8th, for many of the above reasons.