Reason doesn't have an official way to support maintaining sites in
multiple domains from a single Reason instance. There are some hacky and
fragile ways that this can be accomplished (e.g. by dynamically assigning
REASON_HOST), but they are less than ideal, and fail when links between
sites are desired.

The vision:
When a site is created, one should be able to assign it to a domain other
than the default, or do nothing and leave it under the default domain.
Things that will likely need to change include:
-- Site table and URL History table will need domain field added; empty
domain fields will be assumed to be the default domain
-- URL and link-building tools will need to pay attention to the site's domain
-- Administrators can put together an array of blessed domains in a
settings file, which will indicate the filesystem paths of the domain roots

There's probably quite a bit else that will need to occur; those are just
my initial thoughts.