Quick detatch scope rings.
The selection of 35mm scope rings is minuscule.
Rings with inserts, I know Burris makes some, but how about a Canadian company too! Eliminating the need to lap rings, and have a much better hold than conventional solid bases. I would expect more consistent poi throughout temperature change.
Selectable muzzle brakes... I love target shooting with my brake all day but I can not fire even one shot in the field without ear protection or it feels like I've been stabbed in the ear with an axe. Being able to twist a cover or insert to select on/off won't affect harmonics or load tuning but makes 2 rifles out of one.
Contoured/formed picatiny rail covers like wide flat bases for shooting off bags ect.
Waterproof gun cases, like a dry suit with a durable abrasion resistant protective fabric cover.
Slip on cheek/comb risers that can be adjusted with additional insert pads or something.
Bipod feet made from a durable/grippy, foam/rubber compound that is "dead" so it doesn't want to bounce off hard surfaces at the moment of recoil.
Last but not least a product tester.....I volunteer.