currently the 3-way adapter has the bottoms pointing outwards - how hard would it be to get a variant that has the tops pointing outwards?

additionally - have you ever considered making dome structures that are compatible with KPBS corridors?

Hmm, i think dome structures do not really fit into the concept of KPBS. I made some experiments with them a long time ago, but it did not look that well.

Making the tree way adapter to have the tops pointing outwards is possible but does not make sense to me. The Adapter would need to be a lot bigger and it is already a bit bigger than the biggest rocket diameter.

that's fair on the domes.
the use case for the reverse 3 way adapter is primarily for space stations and large built-in-space vessels.