The JP website mentions that they need the best trainers to find out what happened to the site. What do the best trainers all have in common? Evolved Pokemon. They're not just gonna send it newbies, they need trainers with more experience under their belt

The Starters evolutions will be revealed so that they can help with finding the culprit. Impidimp will be the the one who caused all the commotion and Sirfetch'd will be the reveal that's been teased.