One could argue it's a bit indulgent to go even beyond the base MV1-5 forms. One could argue that's mission accomplished, time to wrap things up in a neat and tidy bow (preferably the only thing worn by Grace in while in one of those forms), and move on!
Well, quite frankly, I believe there is great value to be had in expanding on these offshoots! With these things established, that will mean they'll be there for the future, ready to unleash in both canon and uncanon! And there's no reason there couldn't be such offshoots for the female forms as well! It's a glorious, brand new age of transformation possiblities!
That, and I'm not ready to move on to a different story, and this is a FANTASTIC excuse to prolong the storyline. But all that other stuff is true, too!