Are there any planned languages based on Indo-European?
That's a serious question. I'm familiar with the basic theoretical principles behind PIE.
"Truly planned languages" are Interlingua , based on Vulgar Latin, or Interslavic (medzuslovanski). These are essentially hybrid languages composed of the cognate vocabulary of the entire Latin or Slavic language.
Have there ever been attempts – even by individuals – to imaginatively expand the truly reconstructed, fragmentary words and grammars of PIE into a planned language?
If there were/are various pan-movements – Pan-Slavism, Pan-Germanism, Pan-Latinism, Hindutva – why not also a Pan-Indo-Europeanism?
There are some plan languages based on the Indo-European or inspired by them.
Here are some examples of such plan languages:
ChatGPT?