Here are some suggestions I think lots of folks would benefit from:
An easy way to change the words found in the appointments.php without needing to open the file and edit it like "Select a Service". I want to change the word Service to Fishing Vessel and Provider to Captain. I can also see this used as a Tee Times & other reservation system. Therefore, on a WP Network it would be helpful to be able to modify this on a per blog basis. If you set it in the Appointments.php it will go Network wide.
Making it easy to change words like "OUR SCHEDULE FOR AUGUST 2013" to a larger or bold font or H1 etc.
Adding a feature to allow use of Appointment Calendar across various sites / blogs on a Network. For example, a Fishing Vessel and Captain may want a website on our Network. It would be great to be able to just add his Fishing Vessel calendar to his site / blog on the network so it would sync with the main site on the Network. We are looking at over 20 fishing vessels on the main calendar so he would not want the competition on his particular site on the Network.