Any thought of having an instanced battle is counter to what Eve Online stands for which is everyone interacting in in a single shard environment with no instancing. And besides, as the recent battle of the 9-4 Keepstar has revealed, everyone wants to dog pile. Battles are only going to get bigger and bigger which means more players want in on the action. 6,000 players in local is a huge lode on the server nodes already.
So instead of limiting the number of players engaged in battle, CCP is figuring out how to mitigate or keep under control the lagfest that occurs when you have that many players duking it out in null-sec. TiDi was the initial solution to the problem. But of course we know TiDi has its flaws and limits. But fight are better today than how it was before TiDi was first implemented.
Thus CCP is eventually going to be forced to have to rethink their server architecture that allows for bigger fights with more players in local and still have less lag than before. Instanced battles are not an option in the case of Eve Online which is mainly known for never having instanced battles.