Currently the debugServer property in launch.json is at the same level of version - that is, it's global.
In my opinion it would make more sense for it to be under the specific configurations; the benefits would be:

• the extensions can fill launch.json appropriately (as far as I can see extensions can easily provide configurations when they are first clicked in the debug gear dropdown, but not global properties to launch.json)
• debug extensions using programs and ones using debugServer properties could be mixed-up in the same project

Of course there is a high change that I'm missing something big - documentation about debugServer is hard to find and sparse, that being the case, sorry in advance :)