I think it is unlikely that there will be two-way-sync for these platforms any time soon. Fibery is trying to be a replacement for them, so there is less incentive to develop a two-way-sync that would imply that users keep Fibery and Trello (or F and N, F and CU etc.)
I think it’s more likely that the product team would focus on adding features to Fibery that would make it less and less likely that a user needs to also use T/N/CU.