I think that Hatsan (or whoever thought or invented this solution) had a very good idea.
The possible accuracy issues can be easily solved by controled quality of manufacture of the various parts - for example if this system was made by Feinwerkbau or Anschutz the tolerances between parts would be much- much better.
The system can be developed in a way that it could allow easy and fast barrel interchangeability (swap the 0.177" barrel with a 0.22" one or a 0.20" in minutes - without the neccesity of special tools).
It could also be made in a free floating design allowing maximum potential in accuracy.
A clever designer could also add a simple mechanism for adjusting the point of impact on target so the shooter can make scope zeroing much easier (by altering the angle of the barrel inside the sleeve).
Just some food for thought...