Translation:You drink coffee often, while I never drink it.
The antecedent is stated here. To could refer to coffee if you were pointing at it, but once you state it, the pronoun has to agree with it's antecedent.
Looking into this a bit more, it seems that a coordinating conjunction, that ties together independent clauses, does not assume the first position of its clause, while a subordinating conjunction does assume the first position of the dependent clause. And while kdežto and zatímco are considered subordinate conjunctions, apparently they can also act as coordinating conjunctions, as in the sentence above.
I wish it were that easy. There are many coordinating conjunctions that do assume the first position, such as "dokonce, jak – tak, sice, buď, nebo, vždyť..."
Conjunctions that assume the "zeroth" position are pretty much excpetions, but you're right that "kdežto" belongs to the "a, i, ale" lineup.
To make things more complicated, subordinating conjunctions don't care if they take up the FIRST position or the ZEROTH position in most circumstances, UNLESS it's the main verb that wants to follow them -- then they will stubbornly stick to the first position. Let me indicate the position within the subordinate clause in parenthesis:
- ...protože(1) se(2) dívá... (...because he is looking...)
- ...protože(1) se(2) František dívá...
- ...protože(0) František(1) se(2) dívá... (actually more common that the one above)
- ...protože(1) se(2) dívám...
- ...protože(0) já(1) se(2) dívám... (the preferred position for "já")
- ...protože(1) se(2) já dívám... (stressing/contrasting "já", not a neutral position)
- ...protože(1) se(2) často dívám... (neutral)
- ...protože(0) často(1) se(2) dívám... (also fine)
- (X) ...protože(0) dívám(1) se(2) ... not possible!
The above works the same way for other compulsory clitics such as "tě", or "mi".