I spend 90% of my time on my "daily" notes, so (selfishly) that's where I would focus. My challenges there are:
1. My date format is "YYYY/MM - MMMM/YYYY-MM-DD" in a folder called Daily, which means the files have names like "Daily/11 - November/2021-11-18.md" (and surprisingly, Obsidian accepts that date format and manages the intermediate directories just fine). That crazy date/filename format would need to be configurable and supported for (I think) the Journal feature to work well 2. I don't include a heading with the date at the top of my Daily files (actually, _any_ files), so finding the right note (when I see a bunch of cards that all look pretty similar) can be challenging - at least my directory structure means I can narrow down to the month very fast by looking at the folder names 3. Bonus points for a calendar view to make #1 and #2 easier?
I think if I had to pick the biggest challenge, it's #2 because I end up with a big soup of files that all look the same, where the important thing to discriminate between them is the filename.
I also love the commercial model - I love Open Source, but I don't mind paying for quality, so I get the best of both worlds here. And more importantly, I don't have to spend a huge amount of money just to trial the software for a couple months - I can pay the (small) monthly fee, and if I like it, either pay the "full" fee or just keep paying monthly.