Of course, in reality the EU allows Imperial units (we still have pints of beer and milk), fairly exclusively for the UK as other EU countries prefer metric.
However, now we haven't got any influence in the EU they may drop the allowance for joint measurements and insist on any product going into the EU be measured in metric only. Would UK producers who still export want to have one set of packaging for domestic and one for EU? An unnecessary cost I think.
Therefore an unintended consequence may be the disappearance of Imperial measurement of produce altogether from the UK.