Ishgard: Being destroyed by dragons.
WoL: Just another hour now and I will have that fish!
Pulling for it to come in 6.1. I have an on/off addiction to Stardew Valley
For those not wanting to click the link- long story short:
More updates are coming in 6.1 & likely fantasy island is there, as well as hrothgar hair updates & purchasable Ishgard housing (In 6.0, you can only roam around the districts)
Expect Island Sanctuary to be 6.2 at the earliest. Unlikely to be earlier as 6.1 is pretty much set in stone and the Devs are still calling IS as 6.X .
Island Sanctuary can come even later than 6.1. There is a buttload of content to get through at the beginning of an expansion. Closer to mid-expansion when peeps are firmly in place under the new level cap is perfect for this kind of thing. I have a gut feeling that you could basically retire your character with things like Island Sanctuary, much like you could when you could own multiple plots back in the day. I think it's going to be a lot like and was inspired by Harvest Moon.
The expansion announcement includes some content we'll see in the patch series for that expansion. The Island Sanctuary is already confirmed to show up in the patches, but where specifically is still up in the air.
That said, it's probably soon because they don't typically announce late-series content with the expansion.