Many of us use bitcoin only in exchange/trading site, while bitcoin should be more used in marketplace/online shop. Which one do you choose? Do you prefer to use bitcoin on a trading site or marketplace/online shop? And why do you chose that?
In my opinion, it should not be. Just watch bitcoin as gold. As for the means of payment, it is necessary to have specialized currencies to do so.
It will overload the system.
Yeah I think you're right. Bitcoin doesn't seem to be able to cope with the same volume of instant transfers that card payment systems like Visa and Mastercard do. It's still a bit slow for people to adopt it for online shopping at this stage. Certainly, it's being improved, and there could be a means for that in the future, but at this point it is more like gold. You take it to the jeweler, exchange it for some dollars, euros, etc., and then go and buy what you need there.
Not being said that Bitcoin can't still be used for payment. I offer it as an option for payment when clients ask, why not? Some prefer to use it, others look at me like I'm crazy.