I say boy! So far, the Dutch royals have a pattern. The first child is ALWAYS a little girl (with the exception of Carlos Hugo, but I mean in-wedlock babies) and with the van Vollenhoven's, the second is always a boy, so we'll see if Floris and Aimee continue this tradition.
If she has a boy, then I would imagine that Hans would be among the baby's names. It would only be fair, since Magali is named for her sister. I would also like to see Floris adding the names of one (or more of his brothers). Juliana would be appropriate for a girl's name, or one of the names for a girl; especially since the baby will be born in the Juliana Year.
Well, after Magali I am sure they go for another name that does it well on the field hockey club. 'Fleur' would be an option for a girl ... They won't go for anglo-saxon names in a million years, most people with english names are of a different social class.
I do hope that they pick a traditional Dutch name. It would be a lovely tribute to their countrymen, especially since this is a royal child, and both parents are Dutch. I could understand a non-Dutch name if Aimee was from somewhere outside the Netherlands, but she is not. They haven't publicly stated that they know the baby's gender, have they?