Even though the 1 series BMW convertible is not available yet, does anyone know if the Pioneer AVIC-Z2 or Eclipse AVN6610 navigation systems will work?

Whats so terrible about BMW's Nav? You must be extremely picky or have read too many reviews. It's not as complicated as everyone makes it out to be.

No... You only have a single DIN size to work with in the 1 series. The word "DIN" refers to the height available for your aftermarket radio. Single DIN is approximately 2 inches in height.

The 2 radios you listed are DOUBLE DIN sized units.

Your only option is a single-DIN sized flip up screen GPS headunit.

You'll also need an adaptor facia plate shown here.
http://www.justkenwood.co.uk/install/show_model.asp?id=331