The biggest problem with that would be meeting and actually seeing other players, let alone fight them.
In Order to move inside the solar system, you would have to be travelling at speeds that would make flybys of 2 ships next to each other a very short and difficult to achieve event, unless the ship is really really huge.
Even if you had large radar ranges, getting someone in visual range without losing him from view again within split seconds would require you to slow down to speeds where it would take like a minute of trying before you are at the desired position.
And dont even think about pvp at scales like that.