Thank you for posting this, I'd just like to share my point of view as a level 49 Sith Assassin playing on a server where the Empire is mostly dominant.
My friends and I started playing Republic, but as soon as we realized how imbalanced the factions were we rerolled Empire. We mostly PvP now seeing as there is no way we can get enough people to down a world boss or do any challenging 50 flashpoints. I'll admit, that the Empire is much stronger than the Republic, maybe not innately, but just because so many more people are dedicated on the Empire side, or at least, on my server they are.
From my person perspective, I'm very concerned about leveling up to 50. I feel as though I need to have as many Mercenary and Warzone commendations as possible or else I'll be at a grave disadvantage against other level 50s whom already have a set of PvP gear whereas I do not. I've heard Ilum is poor as well, so no dice there either. So I'm desperately clinging to the last few bars I have left before hitting 50, trying to scrounge just a few more measly points of valor out of it. I don't like the idea of people stomping on low levels in the 10-49 bracket, but that's going to happen with or without level 50s, and worse yet, there's going to be no 50s to defend or carry the lower level players effectively screwing them unless they have a very active faction.
My advice? BioWare needs to allow 50s back in the regular PvP pool and try to bridge the gap that expertise creates. I know for a fact that I won't be even able to PvP anymore after I hit 50, so why am I being punished for leveling quicker than others? I thought MMOs were supposed to reward time spent and progression, not condemn it. Let's face it, a level 49 vs a level 10 will end the exact same way as a level 50 vs a level 10 would, there's no sense in completely barring the level 50s from any PvP whatsoever.
Ilum is another topic altogether, and one I can't rightly comment on since I haven't hit 50 yet.
Tl;dr: Allow level 50s to rejoin the 10-49 bracket and attempt to bridge the gap that expertise causes. A high level player vs a low level one will always end the same way, with or without 50s.