There are a large number of feature requests, bug reports, and maintenance issues placing demands on the SCP's time. The implementation of a feature such as this is far, far down on the priority list.
And the interface is just fine as-is. It works, it's moddable, and it has very few, if any, bugs. Contrast this with sections of the codebase like the collision code or even the asteroid code. Those are badly in need of rewrites, yet there is currently no manpower available to rewrite them.
Consider that even with the pilot code, which was not only one of the most frequently requested upgrades but also one of the hardest, it has taken nearly eight years before someone finally finished a robust, capable, and comprehensive upgrade. The multiple ship docking feature is peanuts compared to it.