Welcome to the forum. 
Yes, it’s been asked for a few times. However
30th March 2018 dev stream:
Zantai_GD: hirelings was a feature I wrote a doc for once, but ultimately we decided against it
Zantai_GD: there were all sorts of complications with adding hirelings
Zantai_GD: we’re not adding mercs, no.
If you want mercenaries then play the Reign of Terror mod which is a D2 mod for the game. It has mercenaries in it iirc.