A new Neopet species would be fun, but ultimately I don't see TNT adding any new species; it's a lot of work, especially considering they need to be compatible with every wearable clothing item. Not to mention the bulk of Neopets' revenue is from Neocash clothing items, and when the artists (who are already stretched thin) have to draw those clothing items for every existing pet species, ...
(Sorry, bit of a pessimistic reply... but a new pet species being a lot of work for the artists is more or less why they stopped adding new species in 2006 with the Lutari, and only added the Vandagyre in 2014 - 8 years later!)