Would you say that it is likely that the way this continues with the Chinese exchanges defying the PBOC is, there will be a first arrest/raid of an exchange?
Well, there is no way to not to defy the PBOC at all. "How to train your dragon" has this in the cartoon:
"The problem is HERE!"
"You just pointed at all of me!"
Their existance is an offence.
There will unlikely be an arrest / raid, because that sort of thing should happen before the event escalate to central government, when the central government can always blame lower level for the blood. Since this issue is brought to central (The Lord) as early as Dec 2013, there is no space for bloody action. You won't hear someone buying execution bullet with 0.001฿, sorry. Put to consideration of foreign capital involvement, bloody action backfires PR trouble. I
had speculated the possibility of blood and picturesque scene, but that was in October before PBOC announcement. After PBOC announcement, no blood. Your life is guaranteed.
What more likely is a strong ban, a national 'illegal exchanges cleanse' action to rule the exchanges outlaw and ask them to settle and stop exchange business before a certain date. They may also take down a few non-bitcoin exchanges, e.g. underground stock broker, to weaken Bitcoin's publicity and to incriminate Bitcoin by putting it together with other guilty financial schemes.
The second on the candidate list is a ban from non-PBOC entity (most likely Ministry of Industry and Information or Ministry of Commerce) for any commercial activities related to Bitcoin - this second possibility won't happen in May, because one weak ban after anther weak ban in short interval weakens Lord's image. After all you should fear the Lord, not to play hide-and-seek.
The third is our Lord's backup plan. Question one exchange about insolvency (typically largest of all targets), force it to actually be insolvency, and use state media propoganda machine to paint Bitcoin evil and black, from birth, with news, documentaries, radio etc etc. This plan is really not needed: as "Art of War" said, letting it die peacefully is better than killing it in fight, and thanks to the Internet, change attitude that radically would harm the reign. It happens only if die-hard bitcoin believers started some activities that calls a lot of atention OR the state decide to take down a die-hard enemy similar in influnce of Bitcoin, and by killing Bitcoin in a confrontation, save the need to do it again for a harder enemy (for the time being, the harder enemy is either P2P lending business or Alibaba, but Alibaba is too smart to need a lesson to teach them, so only P2P lending is left). Both conditions for this level of confrontation are unlikely to happen.
The last outcome: if exchanges all choose to go out of the country, or just do business with cash-at-door on tiny scale, or just choose to close (FxBTC), not trying hosting P2P trading, not trying ATM or vendor machines, then PBOC will say nothing more. However this is also unlikely to happen.