I don't think Forbort-Desharnais is really going to be a thing, they are in different groups in camp and haven't been tried at all. We'll see in the pre-season, but I doubt they go that way. It'll be some other setup. Soucy-Desharnais have been consistently together at camp in Group B.
Honestly, even the idea of them both being in the lineup at the same time while Hughes and Hronek are stapled together means that they'll probably spend some time together, which alone is enough to scare me, even if it isn't the main setup (which, despite training camp lines, we don't really know either way). Things never really work out that cleanly over the course of a game. It's not like the pairings didn't get mixed and matched often last season.
Plus, I'm not even really specifically referring to them as a pairing. Even on separate pairings, that still feels like more defenseman who lack speed in the D-Core than I'd ideally like.
If Forbort is the reserve player, however, then it makes sense and sounds promising.