I know you mentioned that you didn't want PvP to go all the way to 50, so here's one posible solution: have a gap of a few levels between the level range for each zone. This way characters would have to do missions or hunt outside of the PvP zones for a couple of levels to be able to get into the next PvP zone.
I mention this possibility because I would really like to see higher level characters be able to get missions in PvP zones. I mostly solo with my lvl 50 Blaster, so I find a little disheartening to not be able to get some badges simply because I don't team as much as the next person, especially since, at level 50, I'm not getting experience anyway so it shouldn't hurt anything if I'm doing missions in PvP zones to get influence/prestige and the badges.
Just my 2 cents worth.
