This is essentially a map thread. The basic idea is what if the primary system was present for every state in the past. For the sake of debate, let's go by this setup: Iowa, New Hampshire, South Carolina, Supper Tuesday, Super South (with the other states sprinkled in between). I'll start with 1960.
1960Red-Kennedy
Dark Blue-Johnson
Light Blue-Humphrey
Green-Stevenson
Grey-Symington
Humphrey wins by a sound margin in Iowa, with Kennedy running in 2nd and Symington in 3rd. Despite this, Humphrey's support is still limited to the states surrounding Minnesota. In New Hampshire Kennedy wins a dominant victory, proving that he may yet be the front runner. Despite the support of the Democratic establishment, Johnson's "Southern Strategy" is viewed by many voters and a regional, not national, campaign. He wins by a wide margin in South Carolina, but fails to equal Kennedy due to his large fund raising advantage and big wins on super tuesday. Kennedy wins the nomination and chooses Johnson as his VEEP, just like in OTL.