I ride my hardtail 29er with slicks much more than any of my road bikes anymore. Have done several centuries and several MS-150s on the rig. I call it the grand marquee of bikes. A tad heavy but floats over the road noise like a dream.
I sometimes regret I didn't go for 27.5 instead -- though IIRC they were hard to come by back then -- when I bought my current ride. Now after 5x the purchase price in upgrades, it's hard to justify another one... But I wonder who rides niners: I practically never take mine off-road, the wheels are just too big to go over stuff easy.