I don't think so. Sure, there will be fresh, squishy meat for all, but it will encourage people to try PvP earlier, get hooked, and maybe keep the action a bit more populated. Remember, it's not just the L20s that are going to want to come in - it's anyone who has a character that's not at cap. Scaling isn't uber powerful, but it's not supposed to be. Nothing can - or should - replace the hard work of leveling and building up a tough freep. And let's not forget all the new monsters that will get rolled up to take advantage of the buffet laid out before them. This could help to revitalize things a fair bit, but it remains to be seen.
Essentially scaling and Moors passes have now removed all limits from the potential audience for PvMP, so that now anyone can participate. That is a big plus if you ask me.