My issue with Lucina was the fact she looked like Marth, which would be reason for Sakurai to avoid including her.
It was a stupid reason, as there are multiple options around that;
1. Do not use Marth's Awakening design.
2. If Marth's Awakening design is used, use Lucina's Great Lord design.
3. Simply don't do anything for the sake of making them have different outfits as Marth neither wears a mask nor has long hair, depending on which route they go with for Lucina.
Since Lucina would have a different fighting style than Marth, it would be painfully obvious who's who to the point that confusion between the two would only be for the truly dimwitted.
As for my stance on Chrom coming in first....honestly at this point, with the fact Lucina has proven to be a more popular character time and time again in both the West and East, Lucina actually has a strong chance to be added in place of Chrom.
EDIT: On Viridi, note that I said I was considering her.
My reasoning about Sakurai going out of his way to prevent you from fighting her merely made me hesitant to add her to the chart.
However, she does seem to have "pet" status not unlike Meta Knight, so who knows.