Microsoft has announced that the concept of add-ins, now limited to Office for Windows, will soon be coming to Office for iPad.
Just like in Office for Windows, Office for iPad will have a side pane that can add more to Excel. Here’s Microsoft’s example of a Dun and Bradstreet add-in to get company information.
Microsoft says that similar add-in features will be added to Word and PowerPoint for iPad in the near future. Beyond that, the same functionality will come to Office for Android later in 2015.
Office for iPad: The Complete Guide Things you should know that Microsoft won’t tell you: using Word for iPad, Excel for iPad and PowerPoint for iPad.
Ideally these add-ins will be consistent across desktop and iPad apps.