He does say "identical", and notes that it basically just makes her a Marth that's easier to use, so I really wouldn't count on major changes.
Anyway, I've been thinking about her viability. Obviously, she has lesser kill power compared to Marth since she has no tipper. While Marth can kill with tipper FSmash at around 90%, she probably needs like 120% for the same kill. That's a big drawback.
However, she may have a couple minor upsides. Marth has always had that combo deadzone around 110% where his combos just stop working because the tipper sends you too far. Lucina won't have that, or at least not until much higher percentages. Similarly, a couple of Marth's attacks have different properties depending on where they hit you, particularly Dair, which is a spike if tipped. If Lucina's Dair is always a spike, that could be really valuable. Those two factors could make her incredibly deadly with the Ken combo. Of course, that assumes spikes even still exist.
Overall I still expect Marth to be quite a bit better, but it's possible she might be somewhat usable.