Please note that the graphics and the physics engine are technically distinct, and thus you can make the planter turn around the sun, but draw it as the sun would turn around the planets, thus merging #3 and #1, and #2 is just horrible, as it blocks all amazing features like asteroid redirection, planet collisions, orbit destabilization etc...
Thinking long term, it is better to stick with the law of physic as it is proven the most extensible feature-wise.
how great would it be to put a giant thruster on a planet and use it as a missile like in planetary annihilation, such thing would be immensely expensive but worth it if you want to destroy a target of strategic significance, like the homeworld of a major corp, but: you can shatter a planet by drilling to the core and detonating more energy that the planet is in theory to use itself: (mass of planet(kg) * g(9.81 for earth)), thus reducing the number of impacts on the planet and thus the damage, or taking control and redirecting it into the sun.
another interesting aspect is the interactions of massive objects in solar systems, it could be achieved by simply applying general relativity to the bodies, thus creating a destabilization. the problem is it would be quit difficult to make stable solar systems, but it can be countered by making gravitational ridges in the space time fabric of the game, thus avoiding important deviation. but wold it undermine the first proposition of the paragraph ? no, the point is to be able to destabilize a planet from its ridge and then let it collide etc...
planet collision, how would you do that? it is too computationally intense! actually, if you want absolute accuracy yes, but the physics are actually very simple, imagine two balls of slightly wet fine sand, and then apply the energy lost in the movement as heat to the planets, it usually ends in lava planet and a large debris field flying off, the debris has to be proportional to 50 percent of the lost energy transferred into 50% of the colliding matter, propulsing it in the mirror of the normal of the surface, like a standard bounce. In voxel terms, you have to delete everything and reconstruct it after the collision has happened, (voxel -> big particles -> voxels) , approximating the bounds of the particles and adding perlin noise to simulate the finer particles falling onto the planet.
