I know Victor is probably sick of hearing this, but if any one type family could really use some extras, it's Gentium.
First, Gentium is one of the few (precious few) free typefaces that really stands up well against large commercial type families. It was built for scholars, it seems, with extensive language support. There are others, such as Cardo, for example. But none seem to approximate Gentium's special quality. Not only that, but Gentium is a study in readability and solid design. The sample pdf gives the distinct impression that Gentium was no small undertaking. Imagine how well small caps and old style numerals would complement the roman and italic.
We have a new Gentium book weight as well, which of course might presage all of the above.
So, my thanks to Victor Gaultney. And here's hoping there's a lot more in store for Gentium and what appears to be its sans companion, Andika.