Hi Jung-Hwan,
By Microsoft Documentation it's saying that Loop App is going to be included in E3/E5 and no mentions of Academic A3/A5 licenses.:
That means Microsoft doesn't have plans for Academic Tenants at the moment, but It is available for them while on Preview.
You also can try to use the Loop App with your personal MS account while on preview.
We hope they will provide us with clarification soon.