With Regidrako/-leki and Enamorus they've made it clear they don't mind adding additional members to legendary trios.
And the Anime just made multiple Legendary Beasts canon, one shiny set one normal, which means either the Ho-oh story is fake for the anime, or Ho-oh resurrected and transformed into new species all Pokemon that died in the fire, not just 3 specific individuals.

SO continuing with the popular, circumstantially supported theory that they were made from kimono girls Eeveelutions, what would Espeons, Umbreons, Leafeons, Glaceons, and Sylveons that burned to death and were resurrected by Ho-oh look like?