Can a scientific article (of an non-tested idea) in computer science be accepted in a high-ranked journal?
Ideas are cheap. Most researchers have more ideas than they have time to develop them. It's the development which has value. Or to put it another way, in order to advance the field you need to convince other people that your idea is interesting, and the fact that you believe it will not be sufficient. Depending on your subfield the way to convince people may be a mathematical analysis, empirical measurement of an implementation, or a combination of the two, but you need something.