You're assuming that a USSR that isn't dominated by Stalin is somehow "Trotskyist". Wouldn't work that way.
I think the point of Lenin's testament was that there should be no "successor". Lenin very vocally favored collective leadership because any one man in control of the party could very easily liquidate his former comrades.
Trotsky wasn't a political manipulator, whereas Stalin was, and that's why Stalin consistently outmanuevered him. Assuming there is a stalemate between competing egos, and collective leadership prevails (what a "Trotskyist" USSR inevitably would look like), then we must examine not just Soviet domestic policy, but also Soviet foreign policy via the Comintern.
Will the various European and American communist parties still go through the disastrous "Third Period", and all of the purges? Likely not, so we're likely to see more cooperation between moderate Socialist/Social Democratic parties and the Communist Left. There may even never be a Nazi Germany in this scenario, and a relatively peaceful democratic transition to socialism may occur in some Western European countries.