One intermediate position might be for WMF to distribute virtual machine images which can easily be installed on any one of a number of different hosting services. OpenStack/Glance appears to be one such system, although ops probably knows better. The current efforts with puppet and vagrant are pretty close to this goal, all that's missing is identifying some appropriate hosting services and closing the documentation gap.
This would also allow our existing community of MediaWiki hosting services to migrate to the new VM-and-image-based model. --scott ps. as far as a business model goes for a MW hosting company, it would be interesting to pattern it after github -- no charge for "open" wikis (mandatory CC licensing, perhaps with ads, perhaps with size restrictions, perhaps some amount of central auth and vandal protection baked in), but reasonable plans for "private" wikis (with flexible authentication integration and https support so that you can integrate it into your company's infrastructure).