A proper 4v4 practice mode would go a long way. 8v8 is not effective for teaching how 4v4 works, and custom matches require 8 people to gather, form teams, and challenge each other; often times, just getting 8 people is tough enough. And SE showed just how little preseason matters when they decided to start S5 without having gathered enough data to facilitate balance changes.

A proper 4v4 practice/unranked mode would really be a great idea, especially at this time when so many new players are taking up interest in the Feast.