They were talking about a change to runes that would promote specialization.
Essentially, it would make runes bound to a skill once used. So you put your crimson rune into magic missiles, it is now a crimson rune specifically for magic missiles. You can take it out and swap it with another, but you can't put that rune into another skill. Additionally, runes would have random stat points associated with them, so that when a skill with that rune is on your bars, you get that bonus.
These changes would force players to consider where they're socketing their powerful runes. As you level, runes get scarcer and scarcer, and you won't be able to just get optimal runes for each ability right away.
While this isn't exactly a locked in "build", it does promote specialization while leveling, as well as adding a goal for players to work towards in the endgame, which is finding optimal runes for all of your skills.
There has also been some mention among the forums of some sort of restriction on swapping skills, such as a scaling cost every time you swap one. This would essentialy allow experimentation/customization early on, but eventually you'll have to decide on a build and stick with it.
I've seen the videos of the changes the runes make. How they are socketed and how rare they are and what not is not what makes a build. It just seems like the runes are probably not game changing in a sense that choosing your runes is really that big of a decision. I bet I could put random runes into random skills and beat the game just fine. The point of runes is to change a spell to your preference of play. However, Blizzard is no doubt making sure that every rune/spell combo is just as good as the rest, meaning it really doesn't matter what rune you put where because it's probably viable.
I am, the Outlaw Torn