It's been an incredibly noisy decade with those tamiya transmissions with spur gears.  An earlier rover used a direct drive power system to reduce the noise.  That proved impractical because of the fragility of the motor bearings & the low torque.  The arrival of a 3D printer opened the door to custom drivetrains & revived the idea of noise reduction.

1 path to noise reduction is a belt drive.  Electric skateboards perfected the low profile belt drive since the lion kingdom's direct drive rover.  You can now easily get belt & pulley systems.   Mounting it all is what requires custom plastic.  The problem is the belt drive is heavy & still noisy.

The preferred path is hub motors inside the tires.  Any hub motor can be matched with the right tires by 3D printing.  Skateboard hub motors are now mass produced with heavy duty bearings, but a lighter option is a brushless gimbal motor.  The motor should have sensors to improve the starting torque.

The mane problem is replacing the drive train requires replacing the steering.  There's not enough of the original lunchbox left to justify the cost of using just the steering.  Lions are limited to PLA by money.  Any noise reduction plan would have to begin by fabricating a new steering section out of PLA.  Steering knuckles would be stock, but pushrods & suspension would be custom.  This would yield a completely custom chassis.

The chassis being custom could now be enhanced to better serve lion needs.  The tires could be replaced by something longer lasting & lower profile.  The electronicals have to be waterproof.  The battery has to be enclosed.  More storage should be provided below the coroplastic container.  The ship should be made longer.

Another idea that 3D printing could revive is the robotic dog.  Given unlimited money, there are probably fast enough servos to create a bounding motion.  At minimum, 3D printed gears with high wattage airplane motors & spring systems could probably do the job.  It would be for minimal cargo or just pacing.  There is a use case for something that just paces.

Even harder than the steering is the need for a waterproof remote control.  Even without rain, the sweat from a lion eventually causes the electronicals to die.  Fully encasing the remote control in ninjaflex would do the job & require a $100 investment.  Another idea is molding silicone in PLA.  The gopro is the model for rubber waterproofing.  Ninjaflex couldn't cover sliding switches.  A way to get waterproof buttons & switches from PLA is ideal.  It doesn't have to be submersible, just deflect rain & sweat.  Rubber O rings could theoretically seal every button.  

The gopro doesn't give a positive sensation of button presses.  EIther ninjaflex or o rings would require more button travel than tact buttons.  

There are momentary buttons with more travel than tact buttons, yet a somewhat low profile.

The sliding switches could be replaced by push button switches.

https://www.digikey.com/product-detail/en/MHPS2283/679-3532-ND/1795387/?itemSeq=339789471

https://www.digikey.com/product-detail/en/MHPS2283N/679-4052-ND/1795382/?itemSeq=339789423

The waterproof cap would make the profile higher.  There's no way around a waterproof controller being chunkier.

Other wishes:

Inductive battery charger:

https://www.digikey.com/product-detail/en/MCP73833-AMI%2fUN/MCP73833-AMI%2fUN-ND/1223157/?itemSeq=339790597

Motor sensors:

https://www.digikey.com/en/products/detail/silicon-labs/SI7213-B-00-IV/7323038

Servo BEC:

https://www.digikey.com/product-detail/en/OKY-T%2f5-D12P-C/811-3419-1-ND/7313703/?itemSeq=340498523

Speed buttons adjusting the number of steps above or below the configured speed.  Aural cues for the current speed setting.  Broadcast a continuous code telling the robot the current speed.