It’ll still be a while before it’s Christmas. (It will still be a while before it is Christmas. The word ‘while’ here means ‘time’. The phrase ‘a while’ indicates ‘some time’. Sometimes it is also preceded by ‘a little’, ‘a long’ etc.)
So, in my view, the sentence is correct.
Can we get a Christmas tree today?
No, it’s still a while before Christmas.
Can we get one on the Fourth of July?
No, it’ll still be a while before it’s Christmas.
Arinker, yes there is a difference. They are different tenses - maybe.
If it is currently 1600, and I get off work at 1700, I can say,
“It’s another hour before I get off work.”
I can also say,
"It’ll be another hour before I get off work.
I don’t know the grammatical rule on this, but conversationally they both mean the same thing.
On the other hand, I could say, “After the meeting tomorrow afternoon, it’ll be an hour before I get off work.”
In this tense, I would not use “It is”.
I would suggest there is a subtle difference between
“It’ll be a while.”
and
“It is a while”.
The second simply states that there is a lot of time before whereas It’ll be a while says the same thing but indicates to the listener that they have to be patient as they wait.