What you wrote sounds fine: " I would like to be considered for a position in the future." Without the rest of the letter, though, it's hard to say whether it flows well with the other part of the text.

Yes it's fine. It's a polite way to finish if you've reject a job offer and if you are still interested in working for the company. If you went for a job interview and weren't offered the job, you could also use the same sentence in that situation.