In that respect, I'm quite thankful to Tesla for pushing the envelop with Panasonic.
1) All the obvious avenues (like simple battery chemistry) are explored and provide no obvious avenues for success
So you can't reasonably expect to advance here. Otoh, we could just stumble on a huge advance.
2) it is perfectly well known how to make ridiculous capacity, light batteries. There's even 2 known ways:
* chemical energy storage
* magnetic/electrical energy storage
In both cases it's solved ... only in the theoretical sense. If we have a way to arrange individual atoms on a large scale (or even 100nm portions of material) and fuse them, we would be able to make awesome batteries. But we don't know how to do this.
So this is now a manufacturing problem where you just won't get anywhere without incredible amounts of knowledge and fundamental advances.
3) What Elon Musk is doing is standardizing existing battery technology and making it widely available.
On the plus side, we need this. The standard batteries from decades ago can be improved electrically (e.g. fast charging by actually having 10000 batteries instead of one big one and charging all of them, which also enables fast discharging by discharging a lot of batteries at the same time, or even charging and discharging at the same time). An electrically complex, but well understood problem.
On the downside, this doesn't actually solve any issues we have with batteries. They're a little too big, a LOT too heavy. Elon Musk's batteries ... are a little too big, and a LOT too heavy.
What exactly do you mean by this? Fuse them in what sense? What advantages would there be at a smaller scale?
But we can't build those designs.