So, i have not downloaded the mod yet but from what i read it looks like the tech and ethics that upgrade border range are useless, unless the systems are really close. Maybe make the tech/ethic decrease the energy cost for the frontier outpost? Just an idea.

The border expanding tech and such still helps , just not as huge since its based on percentage of your border size.

Is it possible to add trading outposts to diplomacy window (like 'transfer system' option)? I ended up with an outpost in middle of another's (friendly) territory while they have one inside of my borders. Resource-wise they seem to be of similar value. What do you think?

I dont think we can mod the diplomacy screen to that level ... Good idea