If you say that something is only a gleam in someone's eye at present, you mean that it is only being planned or considered, and has not yet been properly begun.
The product is still only a gleam in an engineer's eye.
See full dictionary entry for gleam
a gleam in someone's eye
a plan or project that is only at the earliest planning stage
At present, the plans seem to be no more than a gleam in a developer's eye.