Will be a great addition to have two different settings for both events, on joining and on disjoin.
something like this: imgur.com/KrVLQEn
So when they enter in contact they keep track of their neighbors they are in contact with and when they exit the contact threshold they start to blend on a different setting (like viscosity) until they reach a blending limit so a timer occurs that they start to retract their blending meshes back in normal form.
Also a little gravity curvature could give it more realism.
I understand this can be memory consuming because of neighbor list + data and also one way frame movement because of time dependent data, but as a option could be great for some closeups or stylized shots also could have a limit settings for max neighbor to hold and will take the closest in contact. Also will add details on lowres sims.
It could work as an additional functionality in conjunction with XMesh. So on cashing it will do this sort of blending.
Without this it may look snappy on very spread particles, (like water that fell from a glass on a table)