This could be one main reason to start an initiative that will address ANY BUY/SELLER from ANY COUNTRY.
It requires a system with a lot 'technical security checks' - but, absolutely possible.
There are countries that are not supported by Paypal. And, there are countries that the Marketplaces don't deal with. And to cater to the needs of the buyers/sellers from those countries, YES, there can be a marketplace that deals purely with Bitcoin/Cryptocurrency.