Here is a view of the HDD Side Mount (MAC-202) with 5 drive cages installed (20 drive capacity). The TX10 can mount up to 4 of these.
I'll be buying one of these One option that might be nice to see would be to use the space in between the front bays and the XL window/motherboard tray to mount one of these, or indeed any of the radiator mounts. You could even do a door with XL window + ventilated side for extra radiators to be mounted in the main compartment venting to the side. Overkill for most given the number of other places to mount rads though.