You still need drive redundancy in most setups. And my experience with tapes has been that they are not significantly more robust than drives: they break and die when they fall on a hard floor, they get ruined if heated too much.
And an issue that might be gone in the recent LTO era (has it?), but which I met several times: if you need to recover tapes made 5 years ago, finding a usable tape drive for use or sale might be a big problem. The last drive I had I can't connect to a modern motherboard was an MFM controller-RLL drive pair I had in 1987. IDE came shortly after.
Any sane archiving plan will read old tapes "before it's too late" (yes, I know, I know) and re-archive them. I suspect a prime use case for this proposed optical media is archiving what Hollywood et. al. does, which is getting to be rather large (10s or 100 TB per a major film?), put them in controlled environment facilities and then forget about them unless the film is such a success you want to make a new release that needs to go back to the masters, or more material for a "Director's Cut" etc.
That's true. In fact, any sane archiving/backup plan REQUIRES that you regularly verify the integrity of the data, preferably by restoring -- and refreshing that data onto new media "before it's too late". That is true for both tapes and drives.
I switched from USB 2 external hard drives to LTO-4 (see my other comment in this thread for one reason for that generation, which BTW per the LTO spec can be read by an LTO-6 drive) because I wanted multiple copies of my data in a less physically fragile form than hard drives (something I'm willing to routinely schlep to a safe deposit box). And I'm an old timer, bought my first DECtape in 1978 (sic), because it was neat, and then it became handy when I learned the -rf flags to the rm command ^_^. I'm very used to tapes, how they work and don't, what you can and can't do with them. And while I was flirting with hard disk backup almost had a catastrophic loss (http://www.ancell-ent.com/1715_Rex_Ave_127B_Joplin/images/) only redeemed by luck and offsite storage to rsync.net in Denver.
I didn't buy a high end, super fast tape drive, rather an internal HP 1760 EH919 drive, Newegg will sell you one at 2,130, but with some bargain hunting you can get for $1,400 easily (we managed $1,200), and Fujifilm and HP tapes (wouldn't trust any others, except maybe IBM but those are expensive) from them are going for $39 to $42 quantity one, you can of course get better pricing if you buy packs or 20 (or more) and/or go bargain hunting, e.g. 35.45 for the first Amazon Merchant I found with a rating >= 96% for a 20 pack of HP tapes. That's for 800GB uncompressed storage per tape.
Per my other comment I also had to buy a 15K SAS drive, that was $250 back then (late summer of 2011).
And I should note one of the biggest use cases for LTO drives is fast backups for businesses. With of course plenty of $$$ backing hardware to keep LTO-5 or LTO-6 drives happy.