The best analysis I've read so far of Beam's announcement that they'll be diluting Makers Mark due to increasing demand. Makers is currently 90 proof, which is, like, the bare minimum alcohol content a bourbon needs to be taken halfway seriously in this world; the "new," "improved" formula will be 84 proof, which is more comparable with inexpensive mixer whiskeys like Old Overholt or Wild Turkey. So, really, this is less about Makers Mark getting weaker than it finally becoming the Budweiser of bourbon we already think it is, except that it'll still sell for $30 at retail.
Some good news from Risen's post: Makers 46, the newer, smokier version launched a few years ago, will still be sold at full strength.