grammaticality - For as long "as" ... ? When is the last as not used? What are the rules?

I don't know where you heard the second one, but it is incorrect. For as long as (or just as long as) is the only correct choice from your examples:

For as long as it takes...

For as long as we have a future...

As long as (see def. 37) is an idiom which has the following three meanngs:

a. provided that: As long as you can come by six, I'll be here.
b. seeing that; since: As long as you're going to the grocery anyway, buy me a pint of ice cream.
c. Also, so long as. during the time that; through the period that: As long as we were neighbors, they never invited us inside their house.

I'm assuming definition c for the two examples, but definition a also fits the second example. If that is the definition intended, then the for should be removed:

As long as we have a future...