This would not only allow us to see his race and society through fresh eyes, but also offer whole new perspective on his personality and philosophy, letting us to watch him become the universe-changing monster that we saw in full force this summer and possibly gain a new understanding of him.
And as a special bonus, the fact that the story would have to be a prequel also makes it totally safe from whatever happens to the character at the end of Avengers 4, so even if he dies the franchise wouldn’t have to bother with any fake-outs or miraculous resurrections to legitimately bring him back.
It should be noted that the expectation wouldn’t be to have Thanos be the lead of the film — as previous reports have suggested that the relationship between Ikaris and Sersi will take center stage — but he could certainly be included as a key supporting character in the plot, given his significance and importance in the world of the Eternals.