Hello there,
Thanks for your positive responses and apologies for not having seen the APBS interface yet - I obviously haven’t worked enough in Avo2!
In terms of π-stacking and interactions with aromatic and non-aromatic (https://doi.org/10.1107%2FS2052252519000186) ring systems, there are quite a few geometries to cover (see e.g. Fig. 1a in https://doi.org/10.1021/jp504415p), which are not limited to ring-ring interactions. Among other such interactions, cation-pi interactions are one of the types that have received attention (and parameterization) e.g. in the domain of MM force fields.
As for implementation of criteria to trigger representations of such interactions with rings, one could possibly define a placeholder or dummy atom at the center of each ring, as well as an axis through this center, perpendicular to the ring plane, to have a reference point/axis for distance/angle evaluations. It is perhaps the inclusion of such new entities that would require large changes, as you say @aerkiaga ?
Hope the exams went well!