It looks like tribal is still a theme in M11, at least at the rare level, and this card is a good example. I have never seen a lord that rewards you so much for doubling up before, since if you have two, they both make each other indestructible. Though I doubt anyone will read this paragraph until AFTER looking at the card, here it is:
Not the most aggressively costed guy, Knight Exemplar still offers quite the upside with the potential of locking out removal when you have two of them. You just have to watch out for Maelstrom Pulse, though luckily that rotates out a few short months after M11 comes out.
Knight is not traditionally a creature class that gets a whole lot of attention, but it does show up on a few good creatures in Standard:
The most likely home for Knight Exemplar would be in a Mono-White deck, alongside Student of Warfare, Knight of the White Orchid, and possibly White Knight, but the protection it offers to Knight of the Reliquary isn't negligible. Knight of the Reliquary already draws so much attention, making it more likely that you can stick double Exemplar, and if active, Reliquary can also protect Exemplar with Sejiri Steppe. Plus, who knows what sort of interesting Knights may be in M11...
Tribal lords do have do be pretty good to see play, so Knight Exemplar has a tough barrier to overcome. If there is a lord in each color, maybe one will end up being actually good enough, though only time will tell!
One final note before I go: I will be gunslinging at the FrontRangeMagic M11 Prerelease in Denver, so if you are in town, stop by!