My parents just picked up an SL1 for a trip this fall, and I have had a chance to play with it a couple of times with the newest 18-55mm kit lens. I also owned an Olympus OM-D m4/3rds last year for a trip I took.
My thoughts on the SL-1 are that it is extremely light with the kit lens, crazy light. I had to turn the camera on and off to make sure the battery was actually in it when I first picked it up it felt so ethereal. It is very compact from the back, with most of the landscape being dominated by the huge beautiful touchscreen LCD. The comparison to a "full strength" DLSR is similarly beneficial from the front as Lucy's images illustrate. However from the top down things change compared to a true mirrorless solution, due to... well.... the mirror being in there. Since the camera has to be just as deep as your 50D to accommodate the SLR design, it ends up being rather bulky in that dimension. And even the 18-55mm seems pretty big compared to some of the mirrorless kit zooms out there. I have fairly large hands that are comfortable gripping a larger camera, however something about the ergonomics of the grip on the SL1 didn't mesh for me. I found myself holding the camera with only my thumb and middle finger, with my pointer on the shutter and the ring and pinky fingers just dangling off in space. I actually had a better grip on the camera if I tried to shoot with my middle finger, bringing the ring and pinky up on the grip, but that was too unnatural. It was perfectly fine really with the camera being so light, but with a heavier lens on there, it would become a problem. My other pet peeve is that they insisted on putting it in the Rebel family and continuing their now absurd policy of not having two control wheels for manual operation, even though most of their mirrorless competitors now do.
The key difference to me between buying a pint size DSLR for a travel camera v. a mirrorless is the lenses. As Lucy says, you can get the 18-55 kit, the 40 pancake, and I would even add the 55-250 IS, as it isn't much larger than the 18-55mm. But then you are done. After that you are stuck putting huge lenses on a small body, or rather lenses that were properly designed to be used on a larger body and end up visually and mechanically unbalanced on the SL1. If you invest in NEX, or M4/3rds, or even Fuji-X with its quickly growing lineup, you know you have a choice of dozens of compact lenses to choose from, primes and zooms from UWA to Super Tele, and you don't have a big mirror box taking up space as well.
To summarize and wrap up, if you were in the situation my parents were in, looking for one camera to be your primary camera with an emphasis on travel, the SL1 is certainly a good system to invest in. But if you already have an existing Canon DSLR kit and want a dedicated travel companion to leave that kit at home, I just don't think the SL1 offers enough of a space saving benefit over your full size DSLR when compared to what else is available on the market today in the same price range.