Well, if the future species would be only a concept rather than real, our present species must be only a concept too, so compassion towards living people should be deluded. If Buddhists can't plan to minimize suffering in the future, Buddhist practices wouldn't be so useful.

The future wouldn't yet be real, but the point is that it will be. Are Buddhists not permitted to sacrifice some present happiness or peace for greater happiness and peace in the future? Isn't that precisely the logic of trying to attain nirvana? It's a goal-oriented process, and the goal's fulfillment lies in the future.

What I like about Buddhism and about the other Eastern religions/philosophies is their greater rigor in thinking through the implications of enlightenment. I just try to push the envelope in that regard.