I'd like to suggest that ... OK, even if the ineligible corals shouldn't be included in the "three different strains" criteria, that if people have them and want to share them, then they should go ahead and do so, and place them on the "newbie table"
Or have an "untouchables" category in the swap area, and instead of "pick one" per round, we have "pick one + an untouchable if you want per round".
Mostly, I wouldn't mind some xenia and sort of miss seeing them at the swaps! They are always a newbie crowd pleaser!