In the latest issue of Famitsu, Super Smash Bros. producer Masahiro Sakuri was asked about the online lag.
In the Japanese magazine, he noted how "it varies according to your connection" and that "when the controls lag, to put it simply, it's an issue with the connection speed. If you notice it lagging at all times, then there's a high chance that there's a problem with your connection."
Some fans with the Japanese version of the 3DS game have noted how they have experienced issues whilst playing online.
How do you want to see Nintendo shape the online experience in the new Super Smash Bros. games?