I moved out 10 weeks ago. My daughter is almost 5. We have totally as hoc arrangements. I think it totally depends on your child's personality.
I work away during the week, but not every week. So we literally plan houses week to week -as it also depends if one of us has something planned at the weekend. Usually by that I mean planned for her! Visiting cousins, pantomime, a birthday party...
What I think helps is that I've been travelling for work since I finished mat leave, at 12 months. So she was already used to having say 3 days without mummy around. And as our marriage was shit, she was used to being with only one parent at the weekend - usually me, frequently going away with her.
We're settling into something of a default that she's with me if I'm not away, simply because I'm the more involved parent.
She seems perfectly happy with two homes and short lead times on arrangements. I think that's partly a very relaxed personality, and partly that at 4, she just isn't thinking so far ahead herself. We may change it according to her needs as she gets older.
She does - understandably - like to know day to day who is picking her up from school! We tell her every day who is picking her up, and remind her every day when the next change over is - well, I do. Expect Ex doesn't consider it as much.
The other thing that I think has helped, is I let Ex stay in our old house, didn't force a sale (he couldn't afford to buy me out). The new house has quickly become accepted, because she spends more time here. And the old house is already accepted. I think she might have found it harder to feel at home if there had been two new houses (hence no insisting on my equity yet) or if Ex had had a new house but not much child care.
So I'd say don't assume it can't work - my daughter just accepts that she has two homes. But always be clear with her where she is going. She also is very open about saying if she wants to go to the other parent. I think 4 is a great age for divorce, as she's thoroughly self centred and not worried about upsetting us!