I journal regularly. I was fine with it being iPhone only when I was using my iPhone with a Bluetooth keyboard, or mirroring it to my MacBook. Unfortunately, I moved pretty much all of my iPhone and MacBook uses to my new iPad. The native Journal app is just one thing I can’t use with it anymore. My current workaround is writing in the notes app on my iPad, then just copy/pasting it to the Journal app on my iPhone. This work around is ridiculous and pretty upsetting to me. Journal is a pretty basic app, I can’t understand why I can’t use it on anything else.
I've been playing around with Day One and other journal apps in the meantime, but will probably continue doing this method at least until this next WWDC to see if Journal is coming to the other platforms. Almost two years after launch, my expectations are low. I just see this as another iPad weather or calculator app situation.