While summer fruit or ripe fruit may hint that Israel was ripe for judgement or was going to be carried into exile as in a basket this is not the main point being made. In the Hebrew, there is a word-play based on the similar sound of two words: qavis (summer fruit) and qes (end).1 The point of the vision is the finality of judgement – all the time for repentance has come to an end. The plumb-line (Amos 7:7–9) and the encounter with Amaziah (Amos 7:10–17) combined to prove that compassion could no longer be extended; the gavel of judgement must fall.2
1 This is what the Lord GOD showed me: behold, a basket of summer fruit.