My only real complaint about the SL1 was the "rebel" button layout, the inaccessibility of the * button, so BBF was unusable for me,. etc. and the poky AF system.
Given the bodies size, I am not sure how it could be done better/differently for all.
But I agree that the twisty screen, wifi and of course the improved sensor make the SL2 a more compelling body. In fact the twisty screen and DPAF could go a long way towards alleviating my primary AF control concerns.
I agree the BBF button is not very conveniently located and it can trip you up that it is not where you would expect to find it if the SL1 just had a shrunk down button layout with the same basic configuration as its bigger siblings. But I find it quite usable.
It will be interesting to see how the twisty screen and DPAF contribute to ease of autofocus.