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"The project has been shelved" means that the project will NOT be implemented. "The project is still on paper" or "The project has yet to be implemented" do not have that implication.

But "remains on the drawing board" often has the implication that parts of the project might still be changed, as opposed to a finalized set of plans that merely have yet to be implemented.

I'm not aware of any idiom like that. "The project is still on paper" sounds good in English and would probably be understood. ("Remains" seems slightly odd to me, though it's not an error.) "The...