I think federation probably won't be suitable between Leftypol and the Fchannel federated network for these three reasons:
1) Massive posting asymmetry. We get multiple posts a minute for hours every day. Federating with any existing /b/ or /pol/ on Fchannel would flood it. ( >>14348
2) Moderation. Our users have higher expectations of discussion and moderation than many other imageboards, which would be unreasonable to expect the federated instances to aide by. There aren't federated instances with similar quality control, unlike the diverse Fediverse where there are many similar-enough instances who benefit from mutual federation.
3) General animosity. Even if we didn't flood the place, most of Fchannel's posters are either politically apathetic or let /leftypol/ live rent-free in their heads. Neither party is likely to benefit from the other's posts.
It is unfortunate, as federated technology is generally a good thing we like to embrace; we even use Matrix + IRC bridge for chat groups and have tried to join imageboard webrings. It just appears that federating with Fchannel, at least in its current state, would be mutually destructive.