In my experience collecting shf for 3 years now, you can 90% be assured that the avarage will not reach 2 per month. It actually hasn't so far if you take all months together and have the releases divided by them. They're cashing in on the star wars movie hype now and rocketeering this **** out in a measure I've never seen before. The pace they've released this **** is exceptional for Tamashii's SHF, maybe apart from kamen rider (which I don't know nor collect) or Gundam (but that is a franchise with MANY series).
As a DBZ SHF collector who's had to do with 4 releases per YEAR for years, trust me, 1 per month is something to be happy about. Anything over it is lucky.
Nothing's impossible, tamashii can pull off family guy level random sometimes, but overal I'd prepare for the speed with which they release to drop to 1 a month by july. If star wars does exceptionally well IN JAPAN (because tamashii is very japan oriented and in this particular case that actually is thei only official market for these) we may see most of these throughout the next year. If we're really lucky, we'll have most of what was shown by august. If we're lucky on another point they'll be kicking in on star wars rogue one hype next year and I think episode 8 is summer afterward. That ALL depends on hype IN JAPAN.
If there's anything that can keep a rate of 1 per month higher it's variants by reusing molds, tamashii likes doing that. As well as rereleases. In terms of fully new figures, take all months from when vader came out up to when the biker scout comes out in march and I doubt whether you'll get to a 2/month ratio average.
And ALL^^^ of that is even assuming what we've seen will indeed all be released. You might never see that Grievous again. Seriously, not a joke. They show off protos (and dioramas and props) to hype their products. Judge that in any way you will, but it's what they do.
Be cautious in your expectations and see only what's up for PO as confirmed, that saves a lot of disappointment...
Any shf collector can and of course may correct me, but this is my experience. SHF is what I've grown to mainly collect and my collecting hobby at this point is damn near solely a tamashii collecting hobby. It's why I'm on this board.