Lizzie, you're right that I didn't make the connection with Sydmonton, although it sounds like Sydmonton is much more formal than the usual staged reading (which I assume is just another term for workshop) or concert.
It may just be that I rarely encounter new works, and when I do, it's often a niche work written for a community theatre by someone involved with that theatre. In those circumstances, they probably just go ahead and produce the play or musical.
The thing that Gavin MacLeod mentioned about staged readings that surprised me is that he said something about musicals that he thought would remain at the workshop level, and never be produced because musicals are getting so expensive that the producers would try to make their money through staged concerts. I wouldn't be too happy if something like that became common, because the visual aspects of a show are often just as interesting as the book, music, and lyrics.
Audrey, the Phantom Phanatic, who nonetheless would rather be Jean Valjean, who knew how to make lemonade out of lemons.