Official comment

Good news here, we have made improvements to the opportunities kanban to allow the administrator to set a higher limit to the number of tiles available on the Opportunity kanban board in the Admin >> Global Config area.
If your search returns a lot of results it will now show you the maximum number of tiles it can and tell you that not all tiles are displayed rather than simply showing a message that too many results were returned as it did before.
This change will included in our next release expected December 2015.