Only you can really answer that question. As the owner of a Rockboxed X3 I can tell you it is a very nice player in every sense of the word. Whether the X10 will be better and worth waiting for is anyone's guess. Rockbox is not guaranteed on the X10 - everything about it is unknown at this point, except how it looks, including what the native firmware will be like, that doesn't mean it isn't worth waiting for, it just means it's unknown.
If you want a push in one direction or another, I'd say buy the X3 now and enjoy it and if in the future the X10 proves to be better in every way, sell the X3 and buy the X10, if not, you have a great player you can start enjoying right away.