Hi Martin, you can fillet 2 separate unjoined surfaces but when you do that it performs a surface-surface fillet operation which is a little bit different than an edge-based fillet which is more usually used and which requires things to be joined.

Surface-surface fillets can indeed construct fillet surfaces in some kinds of difficult situations where the edge based one can fail, but one reason why is that unlike the edge-based one it does not try to construct corner patches where multiple fillets are coming together. So if you do surface-surface filleting you will usually have to do a lot of more low level trimming and manual construction of juncture areas.

re: Isoparm extraction, that is on my list of stuff to add, for the time being if you need isoparm extraction you would need to use Rhino in combination with MoI to do that particular operation though.

- Michael