Hi Michael,
After some more digging around, here's what I've found:
1) We can download prior versions of SAPUI5 as an Eclipse Plug-in from the SMP. SAP Note 1892536 has the instructions and download links for Version 1.12.7. At least this would allow us to test the supported version of SAPUI5 independently of the Design Studio SDK. I was able to successfully install the plug-in and display the object tree as follows:
When directly exploring the plug-in archive file with WinZip I noticed that there was actually an embedded DemoKit (which is where the API documentation should be) and so was hopeful that a local version had been installed but was not able to find it via the IDE plug-in;
2) Based on the document SAPUI5_InstGuide_V1-4.pdf downloadable from SAP Note 1747308 I get the impression that the DemoKit is installed as part of the back-end SAPUI5 runtime in the UI Add-on for NetWeaver. Section 1.8.3 of the PDF seems to imply that the DemoKit documentation gets installed on the ABAP or Java Server. I guess this could be one way to view the SAPUI5 V1.12 API documentation unless a local version can somehow be installed.
Anyway, let me know if you have any further ideas.
Thanks,
Mustafa.