Native longan is very close to longan. Fruit is same, but smaller. Like a few of the other Dimocarps it suffers from a poor flesh to seed ratio. Some selection could make it a popular edible native here. Also why grafting to Longan sounds interesting. Also fruits at a different time to other longans, as does issau (later). I cant rememebr when alupag fruits, but it would probably extend harvest further. Maybe making a giant Dimocarp cocktail tree could be a fun project, in a fruity frankenstein kinda way.
I've heard the giant seedless lychee grafts easily, so its one you might be able to top work other trees with once it arrives on your shores (surely not long with the relatively relaxed quarantine laws there?)...