Season 1: Genji (DPS)

Season 2: Junker Queen (Tank)

Season 3: Kiriko (Support)

Season 4: Sigma (Tank)

Season 5: Tracer (DPS)

Season 6: Ana (Support)

Season 7: Hanzo (DPS)

Season 8: ?

Seems like it will more likely be a tank or support given that they both have fewer than DPS, but then again there are proportionally more DPS so who knows? Anyway, my prediction for the next mythic is Winston.