Custom types

Are these something that could be possible? It looks like there has been some thought into how they might work (e.g., you can pass in a type object in the client), but there doesn't seem to be able way to specify them on the server. Perhaps there could be a mapping in the options?

It would be also nice to get access to some of the test helpers - the randomisation things and so on. Maybe they could be exported as share.tests?