[Chris is me]

I would be very worried about side loading on the modules. With modules that long, you run significant risk of deflection under load and thus throwing chains, damaging parts, etc.

Parallel plate drivetrains can be a good choice if you have the right combination of resources (or rather, lack thereof), but just know that you end up using a lot of material in the axis you don't need it. Your strength is going to come from your standoffs. If you have any way to add flanges (e.g. making this out of C-Channel) it will add to rigidity substantially. This is especially important on the drop down wheel.

I would significantly reinforce the drop module and shorten the moment arm (try having a pair of sprockets idle on a shaft close to the wheel, that lets you shorten the module without breaking center distances). If you can add some mechanism to transmit side loads through the chassis (i.e. delrin guides physically constraining the module), all the better.

The integrated piston support is rather cool, but not a super efficient use of resources. You end up using more than twice as much material that just ends up being wasted.