You can totally have a 1000 lumen key chain light, assuming you have a battery capable of enough amps. I think DB Custom has a little light he calls the Texas Poker using a 10440 battery that does 1100 lumen.
The thing most manufacturers leave out of the specs is TIME. Of course, some manufacturers specs are total made up BS to sell their product. Still, if you had a key chain light that did a real 1000 lumen it would only be able to run at that for a very short time. Maybe 20 seconds for instance.
The MT09R that Texas_Ace built can do 20,000 lumen, but only for about 30 seconds.
The copper head Astrolux S43S (that I reset the thermal calibration on to keep it under control) only lasts 35 seconds on Turbo (drawing 18A).
So time is an important factor when talking about run times and is often missing from the specs.
The GT that Matt put the gbx3590 in is a massive amount of aluminum that takes quite a while to heat up. It would probably do 12,000 lumen for over a minute. Maybe 1.5 minutes. Something like that. You would only need a flat, finned bottom head and forced ventilation if you wanted a sustained 12,000 lumen which is totally doable. No need for liquid cooling.
I’ve done research on all the really big lights to see what is the highest sustainable output with no moving air across them. Typically this involves a really large light with a lot of surface area to dissapate the heat and stabilize the temp. The Imalent DX80 is the current leader at about 6,000 lumen.
With active cooling you can easily have a sustained 10K to 15K lumen. These lights already exist. Even 30k lumen might be sustainable, at least in theory. If your interested, I’ve got a thread on actively cooled lights here.