Higher-capacity drives are starting to appear on the market (5TB and 6TB models), and OWC has now qualified 5TB drives for the Thunderbay and is offering a 20TB Thunderbay solution.
The specs indicate that the Thunderbay 20TB uses the 5.0TB Toshiba MD04ACA500 (7200 rpm, 128MB cache). Note that the single-drive OWC Mercury Elite Pro is also available in a 5TB capacity. Ditto for the Elite Pro Dual 10TB.
Separately, another high capacity drive now on the market is the 6.0TB HGST Ultrastar He6. MPG has not yet tested either drive.
How to use all that space? Simply hooking up any high-capacity unit is only a first step. Questions of RAID (or non-RAID, and which type), organizing data, which data should go onto fast SSDs vs external HDD storage, backup strategy, etc all are important issues to consider. MPG advises photographers and videographers on the best ways to address all these issues via consulting.