I really wish we could customize the appearance of our MM pets. As for my MM primary wish-list, here are a few I'd love to see become a reality:
1. Supers - Basically, you lead your own squad of superheroes; First tier would be something like blasters or scrappers, second tier would be a defender and tank, and 3rd tier would be a controller.
2. Either a medieval-like group or a D&D-inspired party; 1st tier would be footmen - 1 with a sword & shield, another with a 2-hander, 3rd with a spear/staff (maybe a cleric), 2nd tier would be archers or an archer and a rogue, and 3rd would be a wizard/mage.
3. Aliens - Either your classic "greys" or maybe just use the Rikti; 1st tier would be basic soldiers with energy blasters, 2nd tier would be alien scientists with weird experimental devices that buff/debuff/heal/control, and 3rd tier would be an overseer-type or alien in a powersuit that acts like a tank of sorts for the group.