Edit: Removed my original write-up to double-check something, lost the write-up, retyped a tl;dr version.

This is aimed at Enterprise, not individuals looking for a Signal-like messaging platform.

"Confidential" e-mail implementations already exist in many places. Plenty of messages need to be e-mailed but the contents can't be inlined due to compliance. eg, medical systems send e-mail updates that are just a plain message but the e-mail is just a link to an auth portal and behind that is the actual message. Not great user experience.

But here, is G-Mail already has Google-grade auth and the same auth as Google Vault, so the document can be stored in Vault and in the e-mail the link and payload itself can be automatically swapped when sending or receiving. Smother user experience. eg, vertical product integration.

This is clearly targeted at Enterprise (G Suite, plus half the questions are about compliance). By default, Apps users are able to use this feature, although it can be disabled at the domain level by admins. It is not the actual sending of e-mails in this manner that's the default.

Put another way: If you don't see the point of the feature, you aren't the target audience. It's not trying to be Signal.

I just don't smell anything nefarious here.

Disclaimer: Am Googler, but unrelated to the project. Just heard about it now and have enough experience in this area that the feature's context seemed clear to me.