This, I believe from what I can recall either it was a University Students project or commissioned concept design that appeared over 10 years or so ago never to be seen again.
The standard Watsonian Squire fitting system is evident.
Various mock designs.
Left and right-hand versions.
This is the main feature, using the mudguard as a lift / hand hold, exit low and in front of the sidecar wheel making getting in and out free from climbing over the mudguard and sidecar of the sidecar.
Shame it didn’t make it into production