If rumors are to be believed 5D's content is coming in January, though it could be wrong in either direction. Maybe the Legendary Six will be among the first synchros, or the Superheavy Samurai though I haven't checked if they are part of 5D's or later.
super Heavy Sams are from Arc-V. though if Shi En is one of the first Synchro's Six Sams will reach Meta Status quite fast. Kizan and others will only make Six Sams more consistent (and Gateway of the Six. I'm almost drooling)