On the 'Manage API Keys' page on devhub (bug 1211934) we should add a button saying 'show secret' in place of the secret field. This will make an ajax request to fetch the secret, display it in a read-only text box, then hide it after a short timeout. This will add a little bit of protection by not letting the secret hang out in the DOM if the page gets left open. The AWS key pages have something similar.
We did this same thing on the Marketplace key/secret page which you can see here: https://github.com/mozilla/zamboni/commit/3e9334aa https://github.com/mozilla/zamboni/blob/master/media/js/devreg/devhub.js#L1370
We decided in https://github.com/mozilla/olympia/pull/815 not to add this feature. Instead we'll allow multiple keys and only show the secrets once (bug 1214928).