I have seen the following sentences:
Let's see who wins.
Why not "who will win"?
Let it be decided tomorrow who will win.
Why not present here, then?
I think that both are possible.
I feel that there is a small nuance difference though:
The action is about to take place very soon.
The action is delayed or postponed (by the speaker).
The present tense can be used to refer to future events, often when they form a schedule: ‘I fly to Paris on Tuesday, I’m in Madrid on Thursday and then on go on to New York for the weekend.’ The present tense in ‘Let's see who wins’ is not the same use, but it is probably more frequent than ‘Let's see who will win’, simply because it’s the kind of sentence that is likely to be found in an informal context. It’s simple, short and direct.
In my opinion:
You cannot see into the future, therefore
In other words,
is more likely to mean what most of us think it does.