Parallel writes are a major issue
First off, the number of DVDs necessary to meet the write speed of a single HDD or tape is massive, on order of dozens. Most companies need 4-16 tapes of a few dozen disks writing concurrently to handle a nightly backup window as it is. The power, heat, and space requirements of a massive disk array is simply not feasible.
Then you have to deal with getting media in and out of those drives, appropriately labeled (inline DVD printers), and stored in removable cartridges. Keep in mind a stripe of 16 DVDs would have to be ejected pretty much concurrently, and a new disk loaded into each of the 16 drives before the backups could continue, that's a lot of work for a robot, or a lot of robots.
Then there's data validation... Tapes have 3 heads: read, write, read. As a bit is put on tape as it fies by, it is instantly read the the head next to it. DVD does not work that way. Have to write the whole disk then validate it. This is more complicated when data is spread bit stream across 16 platters that have to be in sync, and parity bits have to be taken into account.
No, its been researched to death. it just isn't viable. The media is dirt cheap, but complicated and prone to data loss. The hardware is massive, and expensive in terms of both physical and power costs. Even 50GB BDR media is not viable, and is used most often for single system archives, or in the medical industry for MRI image storage that is never centrally managed on a server but is too bid for a singe CD/DVD.
As for longevity, CD/DVD media was designed for streaming playback of digitally converted analog data sets (music, video). DVD can hold a music file with no "perceptible" errors for 50-100 years, but bit failure on the disk level is evident after just 60-90 days. In binary data, single bit lost on a disk can be a major issue, so parity bits have to be used at the block level, and they have to be able to accommodate multiple bit failure per block. Hard disks, not being subject to environmental factors like light, humidity, dust, and physical contact, and which are much better able to deal with heat fluctuations, have a better chance of surviving long term.
DVDs archived just 10 years ago have proven unreadable. Many in the national archive have been lost to bacteria corrupting the inner metal layers. Its a devent low cost portable media for short term data transfer (mailing a large file set), but it is a very poor DR media.