The Equinox project has no plans to implement the subsystems specification. The Gemini and Virgo Eclipse projects seem more likely candidates for implementing the Enterprise OSGi specification. I know Virgo has considered implementing it but right now it looks like they have no plans to do so [1].
The only implementation I am aware of at the moment is the one being developed at Apache Aries [2]. The subsystems implementation has not been released yet, but I know they are getting close to doing so.
Equinox typically has left the implementation of enterprise related specifications (Web, JPA, Naming, Blueprint etc.) up to the other Eclipse RT projects like Gemini and Virgo. The Equinox project provides a number of RIs to OSGi, but it definitely does not supply ALL of the RIs for every OSGi specification (there are many of them and subsystems is just one of them). I suggest you post a message to the Aries dev or user lists asking for subsystems information. I know they are working on one, but they are better equipped to point you in the right direction.