There is actually a finished product out there, called
ClimbStation. It has been developed for some time now by a Finnish company. I have had the pleasure of using it a dozen or so times at the local climbing gym, and I really like it. It gives a really good chance to work on stamina, especially on boulder gyms where coming up with longer routes can be difficult.
The system has various programs and the pitch of the climb can be either adjusted manually, or one can let the program change it during climbing. The easiest programs are my kid's favourite (6 year old), because he is still a bit scared of heights, but has a lot of energy to burn.
Quite expensive, unfortunately, but at least here they have offered some sort of leasing service to Nordic climbing gyms, I think.