Back then it was a little bit more easy to port TWRP because the source code was available. However seems that some people already asked for the source code. And I’m optimistic that it will be published in the near future.
I also got my FP3 already. And needed to realize that I’m very happy with LineageOS (for microG) on my FP2 and don’t want to switch that fast to a non-Google-free Android OS. So don’t know why I ordered the FP3 that fast. I feel little like one of these crazy Apple fans 
Let’s see what will come. As I’m still happy with my FP2, I’m patient for that.