According to the this week’s commission press release:
“This proposal is entirely conditional upon the UK also granting reciprocal and non-discriminatory visa-free travel for all EU Member States, in line with the principle of visa reciprocity. The UK government has declared its intention not to require a visa from citizens of the EU27 Member States for shorts stays for the purposes of tourism and business. EU rules on non-EU nationals travelling to the EU, such as those on border control, would of course apply to UK citizens once they are no longer EU citizens.”
If a Brexit deal is reached, the EU’s travel rule would become effective at the end of the transition period agreed between Brussels and London. In case of a hard Brexit, it would take effect on 30 March 2019.
The proposal needs to be approved by the European Parliament and the European Council.