I'd also prefer mugger croc or Chinese alligator

Or Siamese crocodile instead the mugger, as is more common in European zoos)
I don't think that a false gharial would fit in any continent pack, as Asia still have so many other more interesting missing animals. I would say that the only crocodilian that could fit in a continental pack is the american alligator for a North America pack.
The current continental packs come with decorations, in fact they are a quite big part of each pack. For example, if there's an Asian DLC pack, I don't know if it will come with other Asian theme, as we already have two (Indian and East Asian) or maybe will come with less pieces but with more animals. Anyway, even having more animal slots, I would not choose the false gharial for an Asian pack.
False gharial would fit on a pack based on orders, in this case the order Crocodilia. I think that after the continental packs, the packs based on orders or families should be the future, with more animals and with less decorations (decorations related to the animals included on the pack or based on neutral themes).
I really like crocodilians, so for me it would be very difficult to pick a list of which ones I would consider necessary or unnecessary. I would be happy with any new crocodilian added to the game


. Actually, I'm waiting for more croc species to start a crocodile zoo
At the current state of the game, I think that there's no doubt that in the case of crocodilians what we need is a member of the Alligatoridae family, as we already have members of the other two families.