The term 'gamechanger' gets used quite a lot, in a lot of different contexts and not always when it's deserved.
It's deserved here and now because BioWare's updates for SW:tOR in the 4.0 expac are, literally, game changing.
The changes are so deep and so encompassing that they can, and likely will, have a profound effect on how you play the game, not just your experiences in it.
I have a few plans for after the release and I want to discuss one here.
I want to level a character entirely on a starter planet.
I'm seriously considering levelling a new toon as far as I can while staying on a starter planet.
Since the new level-sync mechanic guarantees you'll be getting rewards and experience commensurate with your actual level (regardless of what planet you're on) it's now become entirely possible to level, using PvE content, on a starter planet. True, you'll need to kill a lot of NPCs, and repeat the Heroics enough times to make your eyes bleed. But it's possible.
Although nebulous at this point, my plan is to roll a Sith Warrior and play as much as I can on Korriban.
Ideally I'd like to go all the way to level cap without leaving the planet, but, considering the starter planets are so small, I'm probably going to need to move on at some point (even if it's just for my own sanity).
I'll probably end up undertaking a one-time relocation to the broader pastures of Drommund Kaas, with it's greater variety of NPCs, higher number of repeatable Heroic missions and access to a Stronghold and GTN terminal.
I know something like this has already been done by players who were focussing solely on Galactic Starfighter and rolled up a toon for that game-mode only. For many of them, they never needed to leave the starter planet. But I'm proposing doing this more as a role-play choice than just staying put simply because the game mode you've chosen to focus on doesn't require you to travel.