As a consumer, I would love to see additional child themes available from Theme Hybrid. I would be willing to pay for a theme that had the features/appearance that I wanted.
From the standpoint of designers, this creates two issues.
1. There has to be a large enough market to justify selling their theme as a Hybrid Child theme as opposed to just making a free-standing theme.
2. This creates issues with support for the child theme--clearly Justin can't provide all of the support for these themes.
I don't necessarily have the answers to these questions, but the obvious solution would be to look at other successful models. Clearly from a business standpoint, Thesis seems to probably have the most successful model in terms of marketing a Wordpress Theme Framework.
I personally haven't purchased a Thesis theme before, but they have similar issues to address in terms of selling Child themes and support for these themes. How does DIY address these issues?
I would image that the best way for this to work would be for all of the child themes be showcased at Theme Hybrid at a central location. Designers could promote their child themes at their own respective sites which would link to the main location for checkout.
Approved designers could have their own forum section for unique support issues. Sale of the Child theme would include a revenue split with Justin and a purchasers of the child theme would get membership in the Hybrid Theme Club included in their purchase.
Overall, there seems to be a trend towards affiliate programs for Themes such as Thesis or Headway. These premium child themes could collectively be marketed in a Hybrid Premium Affiliate program.
Quality Child themes could certainly be priced around $87 for this package. This would actually be less expensive than Headway or Thesis since that's the price of their basic package with skins costing an additional $50 or so.
Before any of the regular users get mad, Theme Hybrid could maintain the current membership fee and regular child themes availability for current use of the theme.
Well, that's what I would do if I were in this business... :)