When I was reading the announcement of the v3 I was thinking "dammit I just bought the throttle and now they have an upgraded version?" When I saw the picture I thought "oh. I like mine better. I"m glad I bought it when I did!"
In comparison, the v4 to me feels more like a "CM-lite". I can see why they might think the v4 size is more appropriate -- when I bought the v3 I was expecting something more along the size of the v4, I think, because when I got it I thought "wow this thing is big". I don't mind the size now, though, and every time I look at the thing I'm impressed and pleased. Also with the v4, I'd really miss having the two axis dials.
So yeah, it doesn't feel like an upgrade to me. My read of the announcement (a comment in their facebook post as I recall) was that the v3 will be available for "one more batch". If I hadn't already bought, I'd definitely buy the v3 before it goes away.