I thought about it. We have no experience with these to be honest and our software is prepared for hard drives. I suppose it won't be difficult, but it will require some time.You could try contacting the WD shop, you might be able to secure a bulk supply of either new or refurbished drives.
Also how "offline" is "offline"? Because you could also consider LTO tape? If you could get an LTO-8 library machine you can store >1PB relatively easily. BL543A MSL4048 Autoloader Fully tested inc 2 x Ultrium3000 FC LTO5 Tested | eBay