If G-Gundam was any indicator, I'd say a Gundam X would turn up to coincide when the series is eventually released stateside. 
Same thing with the Turn A, though I really dislike it's design. 
A Double-X would rock though.  Especially if it comes with LED's to make the chest and fins light up. 
As for the Zeta, I'm almost done with my PG and have a KS, so a new MG doesn't hold much interest for me.  Cool that they may be doing it though.  The floppiness is why I didn;t get the original MG. 
I might get a Zeta Plus C when I get the MG Freedom though.  
Well then if there`s no MG Gundam-X, they are available from a different form Gundam SEED    :   
Alie Strike Gundam   =   Gundam X Dv   
Freedom Gundam     =   Gundam DX      
I wonder why the Asrtay desings in some why they look like those ugly evas.