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I'm a moto guy... I bought my first mountain bike about 360 days ago since my knee can't take running anymore. The main issue with wide pegs (front to rear dimension) on a motocross bike would be getting to the brake and shifter vs getting off the back of the bike in rough stuff. If you make the pegs 20mm...

Pivot Pegz... They are exactly what you described here, plus they include a torsional spring to return them horizontal when you take your foot off. https://pivotpegz.com/