I had a similar idea and it's part of my broader TreeXP vision. The concept is to create a tree climbing monastery, of sorts. It would be divided into sections, one for climbing trees, another for tree camping, another for aerial yoga using yoga hammocks and yoga swings, a slackline area to instill balance and harmony and a seriously fun climbing area for kids. I could certainly see having a part of this being done indoors, but only when the weather is prohibitive. A cocktail lounge and a warm fireplace sounds like a nice addition too.
I did some research on this and found an indoor training facility in Poulsbo, WA, (
https://gravitec.com) that provides OSHA Certification Safety Training for At-Height workers in occupations like window washing, pole work and rescue training, etc.. Unfortunately they offered nothing for tree-climbers in training, nor would they allow me to use their facility even with a signed waiver, due to their insurance liability restrictions.
I also checked with my local fire department to see if they might provide access to one of their training areas, for tree-climbing training. Same concern over liability, but I was encouraged to take their initial physical endurance test and sign up as a fire dept volunteer.