This idea has been developed and deployed to Canvas
Question Banks. If you create a bank of questions in a sandbox course and bookmark those banks, then you can use them in any course. But you cannot then copy those quizzes to any other course because the links to question banks are lost. In order to use question banks in various courses, you have to copy the question banks from course to course along with the quizzes. If you later want to update questions, you will have to update them in EVERY course that uses that bank. This defeats the whole purpose of having BANKS.
There should be a central repository for banks. OR when quizzes are copies among courses, the links to banks should be carefully checked to maintain links to the correct banks.
Comments from Instructure
This idea was completed with general availability of Quizzes.Next. You can find more information about the overall project in the Quizzes.Next User Group.
Quizzes.Next is now available for all paid accounts.
Quizzes.Next updates will be included in the Canvas Release Notes.This includes new features, updated features, and relevant fixed bugs. New and updated features will be deployed to Quizzes.Next near the same time as the Canvas release. Fixed bugs may be deployed at any time.