Hopefully thous "Pan Cake" lenses are for real cameras! The 24mm in EF-S and the 50mm in EF.
BTW EF-S and EF lenses would fit a Canon Mirrorless camera ONLY with ADAPTERS!!! IF the EF-S/EF lenses work on a Mirrorless camera, it would be the same thickness of a Rebel and the same height less the pentaprism.
The 1996 Canon EOS IX APS film camera (which used EF lenses) was 132 x 80 x 59 mm, 485 g (with battery) or 5.20 x 3.15 x 2.32 in, 17.10 oz.
http://www.canon.com/camera-museum/camera/film/data/1996-2000/1996_eos-ix-e.html?p=1Not nearly as small as the Sony NEX-5 (which is also APS-C) From the Sony site: Dimensions (Approx.) : Appx 4-3/8 × 2-3/8 × 1-9/16" (110.8x58.8x38.2mm) (W/H/D); 15/16" (24.2mm) excl grip & lens mount
Weight (Approx.) : Approx. 8.1 oz (229g) (excl battery & media) Approx. 10.1 oz (287g) (w/battery & media)
Canon 5.2 long vs Sony 4-3/8 - Canon 3.15 high vs Sony 2-3/8 - Canon 2.32 deep vs Sony 1-9/16 - Canon 17.10 oz vs Sony 10.1 oz (with battery). I Don't Think So !!!
Canon has mentioned making a SMALL camera with a pentaprism which may very well turn out to be a Digital EOS IX.
http://photorumors.com/2010/07/24/canon-small-slr-update/ I personally would buy this over a mirrorless camera. YMMV