We are already able to modify the top navigation for individual entities. However, we can't modify the options selected for either Sales or Service in CRM 2013 On Premise. I want to remove entities that aren't used and reorder the list to reflect the highest usage. Also, this would allow important custom entities to show up at the front of the list instead of shoved in at the end.

I phrased it as supported because there is a ribbon customizer out there, but as far as I know, it's not a supported customization.