What does $2000 more get me with the RX1 that I don't get with the EPL5?

this is the smallest "full frame" sensor with 2/35 lens you can buy.  the other options are full frame DSLRs/SLTs with 2/35 lenses (comparatively huge), or a leica M with 2/35 (still pretty large compared to an RX1, and no AF and such).  if you are looking for something with RX1 specs specifically, then this is a good buy (aka the only available option).

the RX1 from sony's standpoint is that they wanted to show that they could make such a product.  similar to their XEL-1 OLED TV (wafer-thin 11-inch screen that came out in 2008 and cost $2500) and numerous other products, it is sony selling niche products that cater to the ones that want cutting-edge technology that is a bit early for the mass market.

the cost isn't too unreasonable, considering the sensor and glass, but not practical unless this is the only camera you'll need for a long time, or money isn't much of an issue for you.