I think they're going to hate it. Where is the fun in attacking people who are ready, willing and able to fight back in PvP?
More seriously, I think the biggest concern is that new players will most likely keep the PvP tag off...meaning they won't get to do PvP until end game, and then they won't be in the habit, won't have developed the skills and won't have gathered the equipment and inventory they need.
What do you mean..."IF" their numbers take a huge dive?Even if their numbers take a huge dive, there should ALWAYS be enough flagged players to fill a few shards, so this is win-win for basically everyone.