Bitcoin is legal by some countries but some countries still not accepting the bitcoin.
What you think is Bitcoin become legal in all countries?
It will have an overtaking of the fiat and so much transactions would be done through bitcoin because of its known advantages already.
I think bitcoin will not be legal to all countries
This is an obvious fact because bitcoin is not going to be controlled by just one jurisdiction or country. At most, countries might be factionalised about it and that won't also work.