Why is there no doubt? Source? I thinks it's more like wishful thinking...
There are already better batteries on the market then the ones Tesla's putting in our cars. In fact, the batteries Tesla's putting in their cars are of an old deign, but they're cheap and in great supply (compared to the available alternatives). Other batteries are either to expensive, not being produced in the quantities Tesla needs, or the patent holder is a competitor like GM.
Newer Laptops (for example) use flat batteries while Tesla's still using the cylindrical ones. They COULD switch to the flat batteries which would allow them to "fill in the gaps" and maximize the space in the pack. The cylindrical batteries they're using now create unavoidable gaps between each cell. If they were able to fill in those gaps using flat batteries, that alone would increase capacity. However, manufactures are only making enough of those batteries to meet demand for laptops, cell phones, and tablets. Not enough for Tesla to build thousands of cars with.
Another technology is Lithium-air batteries. I'm not sure where the world is with that technology. But the last I read about it they were having wear problems. The cells were dying twice as fast as their Lithium-ion counterparts which means they're not ready for primetime yet. But still, I think someone on here did the math on Lithium-air and the range we could expect from a Li-air battery in a Model S, and it came out to something crazy like 980 miles of range. Lithium-air batteries can store 3 times more energy then Lithium-ion AND they're significantly lighter (which means less weight to carry around). So IF that technology matures, we should see P800+ in our future.
Another technology is Large Format NiMH batteries. Chevron and a company called Energy Conversion Devices (ECD) are supposedly holding a patent on a game changing "Large Format" NiMH battery. But Chevron and ECD are apparently suing each other over it. GM's trying to buy it, but its been locked up in litigation since 2007 I think. The inventor is also making things difficult because he wants to be the sole manufacturer of the battery (or something like that). That and apparently he's demanding that the batteries be bought in such crazy quantities that Toyota can't even afford it. I don't know, but apparently that battery is a game changer but since the patent is locked up in litigation, no one is being allowed to build it. Several companies have tried to build a better NiMH battery without using that patent, but have failed. So when that mess gets worked out I guess we'll see a move to NiMH.
...bottom line; better battery technology already exists. Tesla is just choosing to use an older/less efficient battery because they're inexpensive and widely available. They could (in theory) build a pack with flat batteries right now that would offer greater range. But they would only be able to make a hand full of them, and like Vger said "you really do not need more range!" I've put 15k miles on my Tesla in the last 4 months, and I've only gotten close to 0 a handful of times. The Supercharger network really does negate the need for it.
As for the OP's original questions: They might offer a special pack with greater range... I think they defiantly could offer special pack... but I doubt they will. Unless they're looking to make headlines, I don't see a good reason for them to change a formula that's working out so well for them now. Maybe in 2020, but not now.
Note: I've have not added a source to any of the information I have provided because it is all widely available with a simple Google search. I encourage you to Google and read up as my information is old and the cobwebs in my head are many 0_o
