IMO, corporation rank shouldn't be so artificial as to have some sort of numerical value based gimmick in-game. A player's loyalty to a corporation and the corporation's loyalty to that player are largely human factors that shouldn't be affected by in-game mechanics. You can limit corp hopping by adding restrictions (24 hour hard-set timers to removing roles, leaving corp, etc). Players staying together is not a gameplay mechanic, it's a human bond that is established based on trust and largely subject to a right and proper backstabbing in the right conditions (something we need more of in this game).

I feel that there should be less focus on how to keep players together and more on what separates them. Everyone rings for everyone in PC, it's a fact. Giant conglomerates of freelancers who are "available at the time and ready for a good stomp" isn't something we're lacking right now. What we are lacking are incentives for players to legitimately learn to hate one another, to lose things they've attained, and to be so utterly defeated as to have to start over.

PC as a whole needs to be more tactical and less "good fight". The good fights will come on their own. Just spit-balling ideas here but, something like newer corps only being able to launch attacks on districts bordering hi-sec systems would give plenty of tactical value in having territory deeper into low-sec. Having rewards that benefit having that deep low-sec territory (better salvage/biomass) gives further tactical advantage. You create a reason for players to -WANT- that territory, to covet it and genuinely desire to take it by any means necessary, including carving a bloody path through one's allies.

PC should be a rabbit hole that allows players to go as deep as they genuinely want to go, and fight as hard as they want to fight, with rewards plentiful (not ISK or clones) to allow for continued expansion of one's empire, should they choose it, with risks involved that allow for diminishing returns. A good example: Goonswarm once lost all of their sovereignty in a single day because someone didn't foot the Sov Bill (which increases based on how much sovereignty you have). It's just an idea.