I do like the readability provided by the pattern; however, it isn't a practical solution.
My colleague and friend, John Hume, also created a solution for testing delegation: Handoff. The thing I really like about Handoff is that it follows the traditional test definition pattern.
At first glance this might not seem like a big deal; however, following the traditional pattern is crucial when you want to run a test in isolation.
A large problem with my delegation custom assertion is that you must run all the tests in a file if you want the delegation tests to run. It's possible to create ways to run the individual lines; however, with each custom assertion a new way to run it in isolation must be devised. A far simpler solution is to stick to the common test definition pattern and leverage existing tools that know how to run one test at a time.
The next release of Validatable will include custom assertions that follow the traditional test definition pattern.