It's too early to say for sure but it looks like the recent PLEX price trend may be changing. The price rose somewhat quite recently and has been holding fairly steady since at around 820 million each.
Of particular interest is that for the first time in over a month the 5 day average is above the 20 day average. This is an indication prices are rising (or have risen recently).
Normally I'd consider that a strong indicator the trend is about to reverse and prices start going up again but right now things are still very much up in the air regarding the multi-boxing policy changes.
The next week or so should give us a better idea if the downward trend is going to continue (possibly at a lower rate), if prices will drop even further, begin to stabilize, or start rising again.
Really what happens next is heavily dependent on how well (or conversely how poorly) and how strictly CCP enforces the new policy. And it's probably going to be a while longer before we know for sure about that.
If you think CCP will not be effective at enforcing the new policy, then it's time to start buying now. If you think they'll be banning cheaters left and right, then it might be a good idea to sell before the price starts going back down again.