The familiar triple triangle frame tells you straight away that this 29er is from GT. If you are going to ride a rigid singlespeed - if not, move along, nothing to see - a 29er makes a bit more sense than a 26er: it climbs better, it's more comfortable, and you can use its momentum to keep up with your geared buddies by thrashing it up to speed and coasting while they keep on pedalling.
To tension the chain, the GT's frame uses an eccentric bottom bracket. With the bike's investment cast vertical dropouts, this looks neat. However, it misses the main advantage of such a setup - ease of fitting a rear disc - as there are no mounts. Nor are there any on the fork, although the front wheel has a disc hub. You can't do much with the gearing either, because there's no derailleur hanger. A Rohloff hub should work okay without a chain tensioner, although you will need a model with a torque arm.
Perhaps this is missing the point: the GT Peace 9er isn't really a bike you'd buy to upgrade. It's a cheap way in to 29er singlespeeding. And that's something it does rather well. The effective top tube is 0.5 to 1in longer than that of the other bikes, opening up the cockpit a bit the better to crank away out of the saddle.
In terms of components, the 32x18 gear ratio is as good as it gets. The rigid ride is softened by 2.3in WTB ExiWolfs, which were among the first big volume 29er tyres. The small tread blocks work better on hardpack than soft mud, which can clog them. (You notice traction problems more on singlespeed because of the high torque pedalling.) Those wide WTB rims would take even wider tyres, although the frame doesn't have mud clearance for anything bigger.
Contact point comfort is critical on a rigid bike. While the saddle is good, the cockpit needs bar ends for hand and wrist comfort when climbing standing up.