With that, combined with the best-practice of passing the Request
object around during the request lifecycle,   I wanted to suggest
creating a 'project' and 'plugin' namespace under request , so that
(moving forward) as people develop plugins or write app specific
request attributes there is no issue for collision against each other
or future Pyramid releases.

The general idea would be this:
   request.project = reserved for your app ( or
request.projects.project_name ).  do what you want.
   request.plugins = reserved for plugins that need to attach data to
the request object.  ex: request.plugins.sqlalchemy

The main idea is that instead of using 'set_property', you'd use
'set_project_property' or similar.  Not suggesting that we drop the
current scenario, just that
- the request object has a lot of stuff in it now
- i can see the request object's attributes/methods growing as Pyramid
matures
- i fear namespace collision.

class RequestExtensions(object):
    def __init__(self, request):
        self.request = request

    @reify
    def some_cached_property(self):
        return 'foo'

    def some_method(self, **kw):
        return 'bar'

config.add_request_method(RequestExtensions, 'myplugin', reify=True)

will allow

request.myplugin.some_api
request.myplugin.some_method()

I'm not sure Pyramid needs any sugar over top of this pattern.

these are all good points.