The difficulty is that when you set thing up, we don't know what other platforms you will set up for. Since OPVault (still) doesn't work everywhere, we leave switching to it an advanced process.

We've thought about adding a screen that asks "Will you by synching to devices using 1Password for Android or 1Password for Windows prior to version XX or 1Password for Mac prior to version YY?" and then using OPVault if their answer is "no".

But a mere warning about what metadata is and isn't exposed, without something that people can easily do is just going to confuse most people more than help.