In reply to Neil Williams:
> You can hire an instructor already, and I'm sure those instructors, including ones that normally work for indoor climbing walls, would be glad of that business.
Not really, it's a completely different proposition economically to hire an instructor for a whole day to go to a crag a fair distance away than to book an hour or two session shared with other people at a local wall. You'd pay more for one day than for a block booking for a 10 week session of 'kids club' or 'youth squad'.
I think there is a place for convenient, outdoor climbing on artificial structures within or close to cities. Particularly large cities which don't have a lot of good outdoor climbing nearby. Artificial structures can provide climbs at the grades which people, including sh*t climbers and beginners want, with rock you take what you get. They can also be engineered for safety. Outdoor 'indoor' climbing can be very pleasant on a summers evening, especially if the wall provides barbecue food (and if you are in Germany, beer) - that's why many walls in Europe have some outdoor structures. Some temporary artificial structures could be a way of 'saving' the summer/autumn season for climbing walls when there are heath issues about climbing indoors.