I like the paradigm of splitting accounts and journals better than I like the paradigm of primary and secondary accounts. I doubt it will make much difference in real terms, but I find it a much more intuitive and helpful way of looking at things.

One thing that I would like is the option of displaying the parent account on a journal. I know that a lot of people keep secondary accounts at the moment precisely because they're concerned about privacy and don't want people associating their accounts, but whenever I use multiple accounts, it's generally just because I want to keep content separate for organisational reasons, and I normally have a note along the lines of "my main journal is over at rho" in their profiles. While I wouldn't advocate having this be default behaviour, it would be useful to me if I could just tick a box and have it show up automatically.