I have spoken with a Microsoft support ambassador regarding this issue, I know it's frustrating BUT it's resolved!
When you try to add an exchange on line account that has office 365basic attached, it allows to add to Outlook (new) and Outlook as downloaded but if you have a stand-alone exchange online plan 1 or 2 it will not install to the new outlook and the reason is that the new outlook will be featuring integration which will enable seamless useability be that on line or on a local computer, it's the way that Microsoft is moving forward with all the feature expectation of the modern office environment.
If you have clients - like I do that have exchange online multiple accounts and users have office 365 that they own or an office package on their account.. as long as the office application is valid it will allow you to add exchange on line (1) and (2) to the outlook that comes with the software. It's also handy to know that you can install an exchange online account to outlook downloaded from the tenancy although the exchange might be a stand-alone, for example you may have a tennant with Info@, jordan@, sales@, blake@ and blake@ is the only subscriber to office 365 business standard (not basic) where the rest of them are Exchange online plan (1) or (2) ... they will all work.
There was a glitch in the sense that if you tried adding them 3 to 4 day's ago it didn't work... that was a planned update which included SharePoint which needed time to propagate, it takes time to update millions of users.
I hope this shed's some light on the subject, the granular share updates were definitely welcomed (part of the update)