And increase the performance required of the machine and add complications such as being able to go nearly anywhere, so you have to defend everywhere.
yeah, the old problem.
from a gameplay point of view, I'd say its as much a problem of (sensor) information as it is about movement speed and necessary omnipresence throughout your worlds. consider the following example with a) a system size comparable to the one we have now in the game and phase speed also at comparable levels, but with total view of all hostile jumps, even at the end of the galaxy. then you wouldnt have to worry about defense, because you could probably detect any incursion in time and send appropriate defenses. in turn, very hard to attack if you have to consider that whatever you send may face the entirety of the enemy fleet.
but then of course a number things could be tweaked. first, of course, the range. it could for example only go halfway to the sun or shorter, depending on tech level and your level of investment, you may detect enemies earlier or later. you could also limit the range of jump drives per se, so that any ship needs to make "stops" on the way from one end to other.
my point being, I'd say there are ways to avoid it. hw for example introduced a resource cost, which I didn't particularly like, but which obviously worked. what I did love about the game though was this strange feeling of naval simulator when you always had the red dots scattered around in the sensor manager. you knew something was there, but it could be anything from a scout to a full assault fleet. something like that could be very cool.
from a technical viewpoint ... well, I sorta remember haegemonia, which iirc did have orbits and moons and all, and pretty big solar system maps too. you can argue that there were fewer systems and planets in that game, but tbh I fairly like the way the game managed universe "feel" and openness.
so, while not being a programmer, I wouldnt be too quick to dismiss it from a performance pow.
that being said, this IS a very old thread, and this IS more supposed to be beta for the recent patch, if I am not totally mistaken, so the ideas might be better put in the standard sins forum. or the devs give us a seperate "ideas" forum for exp and sequel brainstorming. bc lets be serious, if they undertake such a radical redesign, it surely wont be in anything short of a sequel.