Something along those lines has been on my mind for years.
In the early 1990s Toshiba used to make a dedicated laptop docking station along those lines. With a couple drive bays, SCSI controller & a few expansion slots. You put the laptop into a slot and it was magically transformed into a fully featured desktop, with everything was connected up via a single proprietary connector.
I would love a modern equivalent, something like an old-fashioned desktop case (but shallower) with a Thunderbolt connection to the host. With say 4x 5.25" optical drive bays, a few 3.5" internal bays & a couple of PCI-E slots and a laptop power output, it would be the perfect laptop docking station (or expansion for a compact desktop/tower).
I've never seen a modern multiple drive enclosure which can handle optical drives - only ones for HDDs in a RAID array (or ancient SCSI enclosures). And it would be very difficult to run multiple optical drives over a single USB connection (even USB 3 is likely to be problematic).
The best alternative I can think of would be to buy a cheap second hand PC (it need not be a fast one) in a spacious tower case and use Remote Desktop (or one of the many alternatives) to control it over a network connection.
Or if the drives absolutely must be attached directly to the main computer, you could install the drives in a bare tower case with PSU (with the ATX MB connector wired to the case power switched), fit each drive with a USB to SATA/IDE adapter, then connect them to the host computer either individually. A USB 3 hub (which could be fitted inside the tower) would reduce the number of cables going to the host, but there is a chance it might not work smoothly with multiple drives in use simultaneously. For reading it may be OK.