It is widely known that 2013 will be the last version of SharePoint. Everything will be an incremental upgrade from now on with customisations decoupled from SharePoint through 'Apps' working off web services.
At SharePoint Conference 2014 the product team specifically announced that there will be a SharePoint vNext released on-premises, released in the summer of 2015, presumably to be named SharePoint 2016.
Apps are being pushed hard for all customizations so as to decouple code from the "core" of SharePoint so as to allow for a better upgrade strategy.
That being said, I do see Yammer as replacing a lot of functionality within SharePoint over the next 2-3 years, but I believe SharePoint as a product (especially as it relates to document management and search) will continue to exist for at least another 4-5 years.
Apps are being pushed hard for all customizations so as to decouple code from the "core" of SharePoint so as to allow for a better upgrade strategy.
That being said, I do see Yammer as replacing a lot of functionality within SharePoint over the next 2-3 years, but I believe SharePoint as a product (especially as it relates to document management and search) will continue to exist for at least another 4-5 years.