Apart from OS detection, one thing that makes sending unicode characters hard on the UHK at the moment is the need for separate macros for each unicode character. For example, it you wanted to create a Greek character layer (like one of the layers of Neo), you would need 26 macros just for all Greek characters of the alphabet - for one OS. Multiply that if you need different macros for another OS. (I am assuming you create one keymap per OS, and user manually switches between them.)
Parametrised macros may be a solution for this. You would bind something like “Macro: send_windows_unicode” with “Macro parameter 1: 00a1” to a key. For different keys, it would always map to the same macro, but different hex code parameter. In the macro, you’d need to be able to do tapKeySeq CS-u $param.1 enter.