I can tell you, I did a solo Q on quick play on my PS4 and I constantly see people typing Ingame chat and even the names of the players were typical PC battle tags and it had no PS account name on the small tag.
At the moment, console players get paired with PC players no matter what.
Edit: I am wrong, thanks to @Trilly, he/she explained you can chat midgame by pressing the options button -> friends & group - > pressing l3 on PS
So you are definitely only paired with console players while playing solo Q.