I like this idea! It sounds fun, and the temporary slot makes sure
you always can visit it when it appears! It would also make users
more active. All in all a great idea. Full support <3
Support, and support for 7th slot, since I know people who grind
Alola and that takes more than 24 hours (you could miss it
entirely).
As for the method of encountering, I was thinking perhaps do
something like Kyruem, where while interacting there is a small
chance for the island to appear in your hotbar? Definitely a lower
chance then getting Kyruem since this would be a permanent
feature.
Also: Recruitable Wynaut and add a Retro Wynaut that can only be
found here (rare shiny chance)
If I'm online and don't respond, I'm probably busy hunting for the
missing semicolon (C++) Game of Mao