I have no idea, I haven't seen the answer to this question, but I'm also curious.
I would think the lvl 5 raids will be much rarer than they have been the last two days. I got a lugia, but still need the articuno, so I hope they're not too rare.
These legendary raids have really energized the local pogo community where I live. I haven't seen this many people out playing since the first month or so