Bombard published a relatively new paper about Armenian and it's role in helping understanding other IE language's phonology

 Bombard published a relatively new paper about Armenian and it's role in helping understanding other IE language's phonology. 

https://www.researchgate.net/publication/329525333_The_Importance_of_Armenian_for_Understanding_the_Development_of_the_Proto-Indo-European_Phonological_System_in_Old_Indic_Greek_and_Italic

There are two competing views about the phonology of PIE. Glottalic theory suggests that PIE had ejectives. They sound similar to Armenian p' t' k' փ,թ,ք. Germanic also preserved ejectives.

The Glottalic theory was supported by Gamkrelidze and Ivanov who made a case that PIE homeland was close Caucasus, because Caucasian languages also have ejectives. 

Glottalic theory was not widely accepted until now. 

After current paleogenetic findings Bombard also became supporter of Glottalic theory. Here his paper. 2016

https://www.researchgate.net/publication/311845230_The_glottalic_model_of_Proto-Indo-European_consonantism_Re-igniting_the_dialog

Now that we know Yamna people had large Caucasian ancestry it is far more likely to think that they had ejectives than to think that they didn't.