In the overall cost of a RRAM chip, deposition of a few hundred angstroms of most metal oxides (eg. TiO2, Al2O3, HfO2, NiO, etc) is not significantly more expensive than deposition of silicon oxide, so it's not likely a cost driver.
If I got it right this is the bulk effect and Rice's study is more related to SiO2 substrates where the formation is on the surface - one of the reasons it doesn't work in the air.
NDR effect is known for many years but the operational device with properties to match flash and be cheap is different thing...
Two more examples, which were previously cited by Blaise Mouttet, infamous Memristor denier:
D. R. Lamb and P. C. Rundle, "A non-filamentary switching action in thermally grown silicon dioxide films", Br. J. Appl. Phys. 18, 29-32 (1967)
Dow Corning also did work on SiO2 ReRAM in the early 1990's (US Patent 5283545).
Interesting claims they have on being first. Others besides James Tour have published recently on SiOx RRAM--Jack Lee of UT-Austin, and Hyunsang Hwang of Gwangju University, Korea with Luigi Pantisano of IMEC. There are also a few published reports from the '70's, one by MJ Howes and another by RM Anderson.
I think the key to a successful product introduction is the controller in front of the bucket-o-bits. As long as the controller interface is such that the CPU is indifferent to what's behind it then they can quickly get competitive products out into the market in standard storage formats. That'll free them up to sell the advantages of this technology over NAND - faster, lower-power, lower costs etc.
ReRAM is the most awaited replacement of Flash RAM if it get successful implementation as compared to FlashRAM. It really need Chemical Engineers and Nano Technology experts working behind the early invention of the possibilities associated with ReRAM.
My lasting impression of MLC is someone showing a distribution with tail bits and saying "this shows MLC capability"..ok.
If the resistance depends on the last voltage applied, that may not be so useful for memory, but maybe for a memristor.
Here is an important detail, many seem to have overlooked :
["The UCL devices also display a continuously variable resistance that depends on the last voltage that was applied."]
Current Flash already allows Multi-Bit cells, so any alternative is going to have to have the same ability, in order to be far enough ahead of flash, to be worth the bother.