Depends highly on the project type but if we're talking about a typical Delphi GUI app you don't need to be worry much if you depend on the RTL/VCL more than WINAPI itself.

I don't know about Emba.'s actual plans but what they refer to as cross-platform should be a proper port of runtime and VCL. They tried this before with Kylix but killed the project for reasons yet unknown to me (probably didn't raise much cash). So at least to have a taste of how things will work out in the future, I suggest you check out Kylix.