If the battery were the only limitation, you could do 10 times that - or more. Example:
Let's say you take an 18650 that can handle 30A continuous. @3.?? volt that's in the order of 100W.
Let's say you have some power conversion circuitry in between that's 95% efficient, or even better. Or you pick LEDs with such characteristics that they're an ideal match for direct drive (battery -> LED(s), nothing in between).
Let's say those LEDs put out 100 lm/W (or more). Multiply those figures and you arrive in 10k+ lumens territory.
But... apart from runtime, batteries are (usually) not the bottleneck. A whole bunch of other factors is:
-The heat dissipated by those LEDs (easily ~2/3 of electric power that goes in).
-The temperature difference that heat flow causes between LED die, LED housing, base it's mounted on, and the rest of the light that acts as heatsink.
-Maximum temperature of the LED die.
-The amount of heat that light as a whole can shed. Perhaps using your hand, air cooling for the rest.
-Amount of heat your hand will accept before you burn yourself.
-Electrical resistance of wires, switch, contact area's, conducting parts of LED die, etc. Most of those can be quite low, but those resistances are there, and they add up.
-Maximum current you can put through bond wires that connect a LED die to its housing.
-If there's voltage conversion circuitry between battery and LED(s), efficiency of that. 90%+ is very, very good. Lower efficiency is much more common / likely.
-LED efficiency drops at higher die temperature.
-Physical size of all those parts.
All of which make that ~1000 lm is a good figure for a reasonable size, 1x 18650 powered light. You'll quickly notice that more powerful lights are bigger - a lot of that has to do with heatsinking issues.
As LED technology improves and that waste heat is reduced, we
may see some 1500~2000+ lm lights in 1x 18650 size (in the future). But theoretical limits to that are approaching too.
Btw: for high lux numbers you just need an accurately shaped reflector...
