Similar to what is present in the game blade and sorcery - a system which would make the player have to move thier body in order to achieve sprinting, this would add a layer of immersion and realism, which if i understand correctly are the main focus points of Beyond Sandbox. having a weapon in hand should slow the player down by a factor of the weight of the weapon, then holding that weapon lower and moving the hands whilst still holding it should give the player the ability to sprint, the sprint would still be slightly slower because of the weapons weight.
there should also be a system that changes the recoil of a gun based on if the person using it is lying, crouching or standing up right, since the favourable position to shoot most rifles is on a slight knee bend, being slightly crouched should limit the recoil of a gun. this would incentivize lowering the posture ,which would then decrease the movement speed, with physical irl action instead over an unpredictable game mechanic, i find it really irritating when my game character slows down when i ADS in a VR game, making that a result of players physical action, which he may choose not to do would make it more rewarding. also the recoil should be influenced by how close the stock of the gun is to the body
the speed of the player would be dependant on four factors, with them being 1. how tilted the movement stick is 2. the players hand movements 3. weapons weight and 4. the posture/position of the player.
If a player has to move his hands in order to move it would make the shooting more realistic and would reduce the need for artificial spread or accuracy changing.
mixing these two - having to move the hands in order to move faster, and a recoil system based on the players posture - would make for a system that is both predictable and rewarding