As of today, access to the app has been unlocked in dozens more countries, including mainland Europe, Korea, Taiwan and elsewhere. Interested if you're country is now included? Niantic has a full country availability list.
Pikmin Bloom officially launched a week ago in Australia and Singapore, before rolling to the US and Canada a few days later. But it's been beta tested for much longer, and I've had access for a week and a half now.
At this point I'm finally starting to see the fruits of my Pikmin growing labours, as my most-interacted creatures are beginning to reveal their inner selves via dressing up in cute costumes (this is the game's big collection mechanic). I'm also really enjoying the scrapbook/diary functionality, and am looking forward to seeing my area filled with other people's flowers too.
For much more on what the game's like to play, as well as words from Niantic on the game's origins, safety features and future, here's my full write-up of what Pikmin Bloom is all about.