How do I inject all implementations for a given service?

got it (simplified)

.AddTransient(p => p.GetServices<IService>())

but you must match the expectation of the ctor exactly so specifically for my example

.AddTransient<IList<IService>>(p => p.GetServices<IService>().ToList())

As of ASP.NET Core 2.0, if you inject your dependencies as IEnumerable<IService> instead of IList<IService>, you can forgo registering the list itself, leaving you with just the individual services registration.