You really have a good idea right there if someone actually make a bitcoin payment shop but there are cons and pros on it yes the advantage is that making bitcoin as a payment is really efficient and very fast. Another advantage is that you don't need to deal with cash and coins it is much less hassle and if someone tries to rob you store they will get nothing because it is in online but there are disadvantages on it. One disadvantage is that even though if you put a big store in a big cities there are still not much people who uses bitcoin. Bitcoin is still progressing to be known around the world if one day it does I think the price of the bitcoin is already sky rocket high and some people will not get them because it is too much for them to buy. So I would say if someone does do a store only for bitcoin start with really really small just to try if it will work and if does that would be great and if it doesn't well at least worth a shot.