I think it could be great if it will be possible to explicitly declare dependencies between services (for instance by setting field Type[] dependsOn in constructor). I've searched through discussion but couldn't find anything similar.

I sort of thing that is more of a documentation thing.

If anything I would think the best way to capture it is as a facet versus an API.

Facet is the way to go. I'll really like to see if it's possible to implement the getter (and sometimes setter) depending on the facet value? This will provide clean lazy loading and DI for Fan.

By getter/setter are you thinking something like this:

class MyService : Service
{
  @inject SqlService sql
}

Yep, exactly :)

Yeah that be nice - I'll have to give that some thought to where something like would work into the architecture.