Interesting... nice observation.
However, I personally feel inclined to believe that said characteristic on the Way to Dawn is meant to indicate a connection between Riku's Keybade and Roxas.
Kairi's Keyblade seemed to possess similarities to Namine. Firstly, the Keyblade possesses a flower design, and Namine's sandals also have a flower design on them. Part of the Keyblade's handle is designed to look like a small wave, and Namine's name is sometimes said to come from a word mean "wave". The Keychain for the Keyblade is designed after a paupu fruit, which is especially similar to the charm that represented memories of Namine in Castle Oblivion.
As for Riku's Keyblade, it possesses that X shaped design that turns out to be quite similar to Roxas' zipper of his casual clothing. Other than that though, the characteristics of the Way to Dawn seem to symbolically pertain to Riku's decision to embrace the powers of both light and darkness and thus existing in the Twilight. Also though, in the concept video, Ven is the one who specifically draws the Way to Dawn. Perhaps this action possesses little to no meaning since it was just a concept video, but there is also the possibility that this indicates a connection between Ven/Roxas and Riku. (of course it won't be as significant a connection that is shared between Namine and Kairi or Roxas and Sora, but it still may represent similarities and connections shared between Roxas and Riku)