Weight constraints aren't the problem. Assuming that two motors could in fact lift the whole 800 grams ...
If you have an odd number of motors, the extra torque in one direction will cause the platform to yaw in the opposite direction.
For it to be stable,
torque needs to be balanced.
The flight controller constantly re-balances torque by re-distributing power between M1-M3 and
M2-M4
If motor M1 stopped, the flight controller will reduce power to
M2-M4 and/or increase power to M3 to balance torque and stabilize yaw.
If you have three motors running, that third motor will end up lifting one side causing the system to flip over.
The platform is balanced. If you have unbalanced thrust, you flip over.
For it to be stable,
thrust needs to be balanced.
The flight controller constantly re balances thrust on all four motors to keep the platform level.
If Motor M1 stopped, the flight controller would reduce power to M3 to keep the platform level which would mean reducing M3 to the same as M1 which is zero.
Tricopters are only possible because the platform is balanced on three arms and the tail rotor tilts side-to-side in order to steer and offset the torque imbalance.
IF you try to run it on two motors, they would have to be the two across from each other over the center of gravity. M1 and M3 or
M2 and M4.
The problem is, those two motors spin in the SAME DIRECTION. See the diagram above.
The torque would be unbalanced and the platform would spin uncontrollably.
In order to do what you suggest, all four motors would need to be tiltable to re-direct thrust and compensate for lift and torque imbalance.
This is impractical and obviously can't happen with a software update.
Although running on two motors at full power WILL cause the whole system to spin like a top and will be completely uncontrolleable, it may be able to stay level and may provide a softer landing than a dead drop from altitude.
Try this ...
Look at the motor diagram in my previous post above.
Now imagine one motor is dead and try to keep the platform balanced using three motors.
Next, try to keep the platform and torque balanced using only two motors.