Why does High-Sec Exist?

I dont think so.

With the impending destruction of Jita, everyone is going to want the next megahub to congeal closer to their own access points.

Time is the most valuable commodity in EVE.

The nascent NS powers with enormous vested interest in Jita will want the next hub to form closer to them. The Citadels in the periphery of Jita are easily replaced elsewhere.