most probably i would like to use it every day for such simple things as buying food or going to the doctor, i want bitcoin to be mainstream
The chances of becoming main stream of payment within 20 years is 100% possible. For me also, it would be more convenient to use bitcoin for everyday life needs. Expecting those days more eagerly.
I also want to use bitcoin for my everyday needs in 20 years, like you said after 20 years bitcoin would be the mainstream payment system. But now itself I'm able to spend my bitcoins for my everyday needs with my bitcoin debit card. So, after 20 years we can expect more economical meaning for bitcoins.