Sakurai admitted that it's cheating to call Ken an echo. That's why I think if there are any future echoes, they will only have as many distinctions as Chrom.
-start making a Ken echo for Ryu because of course
-decide to change his specials to better reflect his SF playstyle
-decide to change his attacks to better reflect his SF playstyle
-go way past echo but decide to just keep calling him an echo because that was the original plan.