I’ve been using Obsidian in place of DayOne, and for the most part, it works well. My daily is an iPad, so I use shortcuts to populate the notes with some of the info that DayOne does.
I have been using Obsidian next to DayOne for a while before deciding to use Obsidian exclusively. So I set up my daily notes (and weekly and monthly recaps as well) in Obsidian. After about 6 months I switched back to the combo: Obsidian for my note taking and DayOne for my daily journal. Obviously, it is about the ‘why’.
Obsidian appeals to my left part of the brain. It is rational, is favours mental processes and so on. DayOne appeal more to my right part of the brain: I like the user interface better, I like the ‘on this day’ functionality, … So rationally I am appealed to Obsidian and emotionally I lean towards DayOne.
DayOne has more functionality for journaling out of the box. There may be some plugins for Obsidian, but I like the concept of out-of-the-box better than a (sometimes rather huge) collection of plugins.
One size fits all (Obsidian for all you are looking for) may work. And may be a good policy for many or most. For me, I trust my right part of my brains on this one. It’s part of me too, you know.
Hope this helps. And whatever you use: happy journaling. It’s not about the tool, it’s about the journaling.