Some 29/27.5+ forks will take 29x3.0 tires. I run Bontrager XR2 29x3 (Chupacabra) front tires on both my 2017 Stumpjumper and 2018 Levo which have 29/27.5+ forks. There's ~12mm clearance between the tire and fork arch on the Fox 34 of the Stumpy and ~9mm clearance on the Levo's Rockshox Revelation. No frame contact at bottom out. Sadly, neither bike will accept a 29x3 tire in the back. (The Stumpy will take up to a true 29x2.6 tire and the Levo up to a true 29x2.4 in back.)
To compensate some for the extra height of the 29x3 tire vs the stock 27.5x3 tire (~35mm diameter, ~17mm radius) I replaced the 150mm airshafts with a 140mm. The front end is still ~7mm higher, the head angle ~0.5° slacker, and the bottom bracket ~5mm higher (a benefit!). I left 27.5x3.0 tires in back, and I really like the handling of the "79er"! Rollover is improved, and the ride is noticeably smoother. The increase in trail (~1cm) also seems to add stability and makes for smoother carving. I don't sense any wheel flop, and turning remains sharp and controlled. I think the 51mm offset of both forks allows the larger wheels to handle well, whereas the stock wheels may have been better with less offset to provide more trail.