So in other words... someone could do a new PM module if they wished?

Thats got a lot of potential for a later day

A new PM module, a new User management module, a new Groups management module, the Banner management is a prime candidate for next core feature to be put in a module, mail users could as well (mail functionality should be in the core - but why should the interface for mailing particular users/groups be in the core?)

The reason why the PM and Profile modules are in the core is that they are managing core features that are very important.
The Profile module manages user registrations and user profiles - which is a key part of the system and expected to be present even in a vanilla installation.
The PM module manages - as mentioned - a part of the core that is not 100% separated, yet, but once we find a solution to it (so that the notification code does not actually send the PM or mail, but just use a "service" to dispatch a message and leave it to the "service" to determine how to do this) I see no reason why it should be considered so tightly integrated with the core that it cannot be done in another way by another module.

That is the goal, that is the dream - and given time, we will wake up and find that the dream is real.

I am in preparation for working on an orders and payments module, which will be used for the efqDirectory module. I would like to make it easy to use for other modules as well, perhaps for the banners module this would be a good asset as well.

The module will initially be able to handle Paypal payments as well as subscriptions, but I hope that it can be extended soon to use with other gateways as well.

Here is the development link already, but nothing to be found there yet.

Martijn