There is certain uncertainty about O365 and Open Value or Open Value subscription (OVS) with O365
Software Assurance is the key, not just EA clients can benefit from a lower cost of Office 365 but also the Open Value (and Open Value Subscription) you can benefit if you have the company-wide option.
Cloud will be more accessible and adopted at tyour pace adding the O365 functionality and not paying for the full price as the investment on Software Assurance compensates.
if you own Core Cal is entitled to get O365 E1 to E4 at a lower price the same for Enterprise CAL owners.
What about Office Professional Plus? if you own Software Assurance E3 and E4 can be acquired at a lower price
What happens in the Renewal time?
If you want to continue the Open Value (or OVS) then you will be able to subscribe at a lower rate to O365, however if you decide to go totally to Office 365, you will need to still get the Windows Server CALs on premise to maintain workloads.
Core CAL includes use rights for Exchange and SharePoint
Enterprise CAL includes use rights for Exchange, SharePoint, Lync, and Forefront