I expect Apple and/or Microsoft to address the issues with Outlook 2011 shortly after El Capitan's release, if not sooner. Hopefully, getting this to work won't require Exchange server changes, because that will take longer in some organizations.
I have no desire to go from Office 2011 to 2016. But if, for some reason, Outlook 2011's problems with 10.11 aren't addressed soon, I wonder if Outlook 2016 works properly? If so, would it be possible to run Outlook 2016 side by side with the rest of the Office 2011 suite?