The next big Office suite, also known as Office 2016, will be officially announced in the second half of 2015. Although Microsoft has been optimizing Office for mobile, the new Office 2016 will be targeted towards desktop computers and first screenshot confirms it.
The screenshot don't reveal much, only a few new icons that match Windows 10 design. Along with the screenshot, some of the features have also leaked:
Forecasting functions
Time grouping for model based Pivot Tables
PowerView over an OLAP connection
Data model PivotTable Automatic Relationship Detection
BI in Excel-Bi features discoverability
Updated Backstage UI
Rename tables, columns and measures in Power Pivot and adjustments of the PivotTables
Data cards
Skype for Business