We are slowly growing our print farm and currently run it 100% off of Repetier-Server and Repetier-Host. This works well when you have a few printers, but we are noticing some shortfalls.
For starts, it is awkward to change printers in Host. You have to open the settings, select the printer, copy the config, etc. I feel this could be streamlined to make a single drop-down menu on the "Object Placement" page.
Secondly, it would be nice to see more settings that can be attached to the selected printer. For instance, some of our printers use one starting G-Code, and others use another. It'd be nice if when you switched to this printer, it'd only show slicing profiles that are tagged as okay for that printer. We have to keep 15+ profiles for all the printers and configurations, and that can be simplified to just 3 visible at a time by doing this. Some examples of settings that need to be changed are: Overhang settings, Start/End G-Codes, Max Fan %, etc.
Thirdly, after copying the printer config from the "printer settings" page, closing this page minimizes Repetier-Host. Again, a mild inconvenience, but when you are trying to prep 50+ files on 10 printers, it gets annoying having to go and find the Host window after each change.
Fourthly, when changing from printer to printer, especially if you go from a Serial connection to a printer connected via Server, the "Manual Control" page get really weird. It'll start showing a mix of both running G-codes on the bed, and the temperatures displayed will flash between what the two printers are running at.
Lastly, and I am sure this one will be much harder to ever implement compared to the others, but the ability to have multiple servers all tie into one interface would be nice. Currently, each cluster of printers has a Raspberry Pi running Repetier-Server, but it'd be nice if all of the printers and files from all of the Pis could all be accessed from one main page. The only way we can see currently to get a similar result is to run USB cables all the way to each printer from a single server, which is a bit difficult to pull off.
These are not huge issues for myself or anyone here who is trained in how to do it, but my concern is when we start rolling out Host and Server for customers who want to manage multiple printers. If they select the wrong slicing profile and the print messes up because of that, we get blamed for their ignorance. The new UI was a major step in the right direction in terms of "idiot-proofing," and these few tweaks would make it even better!