Testing https://owebapps.nexusis.com/hosting/discovery successfully shows the xml markup.
The Lync 2013 client receives a Error - Connectivity issues. The Lync 2010 client is able to share PowerPoint presentation as it connects to the conferencing MCU in the same way it did with Lync 2010 Server. The WAC server must be discoverable or PowerPoint sharing is completely disabled. You want to see Event ID 41032 that reports back Office Web Apps Server URLs. For example, you should see something similar to this:
Web Conferencing Server WAS discovery has succeeded.
WAC internal presenter page: https://owebapps.nexusis.com/m/Presenter.aspx?a=0&embed=
WAC internal attendee page: https://owebapps.nexusis.com/m/ParticipantFrame.aspx?a=0&embed=true&=
WAC external presenter page: https://owebapps.nexusis.com/m/Presenter.aspx?a=0&embed
WAC internal attendee page: https://owebapps.nexusis.com/m/ParticipantFrame.aspx?a=0&embed=true&
So you check this event ID and can't figure out what's going on. That's when we hop to the WAC server itself and look at event viewer. We see all types of wonderful 1009 and 2009 failures.
To make a long story short you need to install .NET Framework 3.5 on Windows 2012 from server manager specifying the path to the files from the Windows 2012 disk located at \sources\sxs. Seems to be an undocumented step.