While certainly not the first time something like this has been suggested it does seem a bit odd that nothing has really been added to address the issue at all...
Perhaps beyond wanting new sprites there could maybe be some thought put into how to implement it...
At the moment the 3 Sprite tutorial/showcase missions are paired with the Alchemy tutorial missions in the 2-2 mission page...
Maybe.... the pair of new sprites should be something you can get later in the game.... The 10-1 rank mission page has 2 extra slots available on it's page... AND "The Collector" monster also makes a second appearance in the 10-1 mission "Breaking in the Recruits"
Wouldn't it just be perfect to have a new sprite given to the player at this time? One as a reward for defeating Vanaduke and reaching the core, but also it would help explain why the Collector has returned...