It looks like JUCE detects what host a VST3 plugin is running in by the filename (in juce_PluginHostType.h). The sdk provides the IHostApplication interface however, which has a GetName() function that provides this information as well. Wouldn’t it be better to use that, when available? The filename detection could still be used as a backup.
For example, the filename of FL Studio is different on Windows and on macOS. The current check will not detect that FL is the host, while the GetName() function will return the same string in both cases. It will also provide the same name for its plugin bridge, which is also a separate case in the current JUCE code.
Fwiw, the VST2 sdk also provides an opcode to get the host name: audioMasterGetProductString