It isn't currently available yet, but have you seen the MBI Torpedo? AAAx1 sized, the goal is 500 lumens with modes. Not 2000 lumens, but there's not much competition in this super tiny size class.
A couple of samples hit some CPF users, but it's still under dev.
http://www.matchboxinstruments.com/collections/in-development/products/mbi-torpedo
If you don't mind it being over twice as thick as the Fenix LD50, there is the Nitecore Tiny Monster 26 2015 model. It claims 4000 lumens. It's a soda can light.
If you don't mind thermal shimming a P60 module in a flashlight head with an aggressive cooling bezel (like the Cryos Illuminations M2 with big fins,) then maybe 4,400 is possible in a 2 cell light with a quad emitter. You'll want a copper pill and probably a copper head as well. It crushes aluminum in thermal properties and brass is a joke in comparison. Runtime will not be... good. This is to be expected when you're drawing 10-15 amps. Some batteries can handle up to 20 amps, but most will tap out before that.
There's plenty of big lumens blasters, but when you want a small one it really narrows the field.
A new upcoming high power emitter series XHP50, XHP70 should be really interesting. Eagletac and Nitecore are coming out with one. I'm fairly sure they'll end up being bigger than the LD50, though the output should top 3k lumens per emitter.
At time of posting, some of our local CPF modders are hard at work coming up with ways to use the XHP emitter series. I'm sure they'll get it smaller than the big bruisers.