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When the ship lurches, you want the player to lurch, too, not just stay rock solid on the ship's deck. In fact, gravity doesn't change when the ship moves, but the ship changes. If you run an actual physical simulation, it would be simpler to simply change the ship, keeping everything in world coordinates, because the physical simulation will take care of everything. ("having to update all the objects" is not a problem -- because they are simulated, they are updated every frame anyway)
I see what you're saying here, but this doesn't really affect the relevance graph, unless you consider falling from one POR to another. It does affect the physics layer for player position checking and may alter pathfinding hierarchies.
The effect you're describing could be achieved by using a matrix stack to concatenate transformations as the hierarchy is traversed, effectively giving each POR a transformation specific to its orientation and position.
Rather than simply having position, a POR has a matrix (or quat/vector) to dictate where it is. In most cases there won't be any rotation, just translation, since blocks are easier to work with in design terms.
The most complex objects, in terms of physics abstraction (collision hull), at any time on the server are likely to be static POR geometry sets. Other items are likely to be simple boxes, particles, spheres, cylinders, or self-righting cylinder entities such as creatures. I don't intend to implement rag-doll physics on the server, nor do I intend to model 'long footprint' entities (think a horse from above). All of these are transformed by the matrix stack.
In order to lurch (or indeed rotate relative to gravity), we do actually need to inverse-transform the inherited gravity vector which will dirty the physical abstractions for the POR. New accelerations can be calculated for them and they can then update as normal. Route paths for certain movement types will have to be recalculated based on the altered gravity vector (a floor may become a wall) so angular tolerances for paths on the route finding node map must be checked.
Since self-righters will have to self-right, a player associated with the simulation entity can receive a 'I have self righted by [optional quaternion]' message to make their avatar 'stagger', in full on Star Trek styley. The quaternion can be used to determine direction of stagger. Immediately following may be an 'I am falling' message.
Any POR can specify a new gravity vector - although this is intended for spaceships with no global gravity vector - allowing us to model artificial gravity environments but NOT centripetal force environments.
