+1 That was my first thought when I read that post.
If capacity is all they were after, which I doubt since they'll also benefit from simplified manufacturing protocols, I'd have preferred to see them chosing the 26650 format. The reason I see here behind the 20700 format is that it's area/volume quotient (cooling, power delivery) is not so far off the 18650's one. 
Cheers ^:)
Tesla is spending craploads on R & D to increase the power of these cells. Given the rush to produce, they have most likely not incorporated even a part of the changes they are looking at in the lab into the finished product yet. Interesting times indeed, I’m looking forward to it. Musk quoted about the speed improvements based on the new battery packs from yesterdays BBC article: the cars “… hailed the upgraded battery as a profound milestone….will do 0-60mph in 2.5 seconds”
http://www.bbc.com/news/technology-37171455
Given the rush to production I think it’s possible we’ll see availability within a year. Hard to say as none of us know the production details of the battery’s. That means that 4-5 years might not be unreasonable either, but I doubt it will be that long. They have a bunch of pre-ordered cars they need to build first ASAP though.
A few years ago, I had read that Tesla would have chosen the 22650, to replace 18650. have changed their idea.
I like more the 22650 to replace the 18650; It is not fat like an 26650 and can reach (and archieve) good capacities …I think
It might not make sense in terms of capacity/cell but if the added capacity brings down the number needed then it makes sense, especially for vehicles using thousands of them. Then there’s also the power wall technology that will demand a huge number of cells.
So, do we stock up on 18650's or sell off our 18650 flashlights as quick as we can, while they are still worth something? 
Ohhh - maybe the new BLF Q8 can be tweaked to support 4 20700's? 
Yes Tom let’s go for a thick walled tube 
But with the demand from cars , build by car manufacturer I think it will be a while before 20700 get available for us
Cool they spec 700 maybe the longer 18650 and 26659 cells will be labeled 18700 and 26700 soon!
The 18650 battery will be around for a long time.
Only Tesla is committing to a new size, so unless everyone else is going out of business we are safe.
I could be wrong, but I believe the “breakthrough” Musk was talking about is the new cooling system that will be utilized, more so than the individual battery itself. I think it’s the problem Honda is having right now with their new hybrids. The cooling system is poorly designed, the cells heat up and lose capacity, thus less than expected fuel mileage. Note in the BBC article Musk says, “in cool weather, a driver could travel from San Francisco to Los Angeles - a nearly 400 mile drive - without recharging”
Tesla and Panasonic are committing, that is... We just don't know how committed Panasonic is, and if others will follow.
Maybe they are hollow like the Apple cells recently discussed (with the hollow space for cooling.)
Can't wait to see how it develops. Some of the 18650's are already close to 20700 dimensions ;) I believe most torch walls could be bored out by a milimeter without a problem to fit the new cell if necessary and worth the effort in terms of gained capacity.
First link is about “graphene batteries” and is surprisingly un informative. I have searched and not found any info about what this battery actually is. They do have very impressive claims. I would not believe them, however. Battery “breakthroughs” generally do not happen. There is incremental development and improvement. If this particular graphene battery technology was really promising, lots of labs and institutions would be developing it.
Second link is old, and about the development of a type of Li ion battery, LiFePO4, that A123 pioneered.
The cells that will be made at the gigafactory will very likely be traditional Li ion chemistry.
I think it will be some time before the 20700s make their way outside of Tesla’s supply chain.
I found these in a provided link a week ago and it was new information to me.
From my meek understanding battery technology and developments are not made public, and in fact much of the new Tesla manufacturing information is being kept secret and proprietary.
I may have confused the claims in that video with some other graphene battery claims I read somewhere else. The “G-king” battery in that first video is apparently an 18650 format cell with ~1200mAh capacity and 3.2V nominal voltage. I wouldn’t be surprised if it was a LiFePO4 type Li ion chemistry with a bit of graphene in the one of the electrodes.
If you can’t tell, I’m a bit skeptical when companies use graphene’s “amazing properties” to market a product. Graphene has some interesting fundamental properties, but in my opinion mostly of academic rather than practical interest.
This site says “In stock”.
http://www.illumn.com/20700-sanyo-nc…-flat-top.html
20700 Sanyo NCR20700B High Discharge Flat Top
SKU:Sanyo NCR20700B
Availability: In Stock
$9.99
PRODUCT DETAILS
SANYO NCR20700B 4250 mAh High Discharge Flat Top
Specifications:
Nominal Capacity: 4000 mAh
Typical Capacity: 4250mAh
Nominal Voltage: 3.7V
Standard Charging Current: 2A
Discharge End Voltage: 2.5V
Max Continuous Discharging Current: 12A
Weight (max): 63.0g
Dimensions:
70.3mm (L) x 20.35 mm (D)