I live the concept, but don’t think it’s remotely workable
What I would rather see if the maintaining of the 2m rule for pavements and public open spaces. So that it’s no more unsafe than currently, regardless of time or place we want to use our new concession of outdoors exercise.
Business premises could of course be freed to set their own distances, as we wouldn’t be going Inside anywhere anyhow, so it needn’t be a drag on other people.
As you cannot tell who needs to shield by looking (no age categories, and only some of us have visible disabilities), then keeping 2m from strangers outdoors is safest and we’re accustomed to it.