You don't need them to. Put the pink in the more defensive that you may or may not be able to defend. If you move up, place a trinket in the more immediate area.
Scenario: You are blue side bot lane. Put a pink in your tri-bush. With that covered, they can only come from river, or the enemy lane (or from behind your turret, but if you're getting clown fiesta'd the trinket won't tell you anything that overall map awareness hasn't already). So if you move up, trinket the river. Things change if they have Eve or any jungler who can come from the enemy tri-bush (Shaco, Rek, Lee, Zac, J4, etc.); play accordingly. Same for red side top lane.
On the other side...same thing, actually. Pink your tri (it's not as defensible, but it's better to have constant vision of that than place it in non-defensible positions like a lane bush or river) and trinket the lane or river if you move up.
After lane, it's a different story. But you mentioned ganking angles, and the system we have now covers them just fine.
As for mid lane...I don't even know, man. It's not as formulaic. But I know you couldn't cover all six ganking angles last season and you still can't this season, so it's a moo point.