thank you for the link. It's at 12:28 in the talk where he mentions the firm is Conning, who used k for financial simulations for insurance. In this talk, he doesn't suggest he is working with other firms to replace k/q/kdb+.
Do you have a link to the talk? It would not make business sense for Stefan to spend time replacing the small percentage, if it were indeed a small percentage. Actually, kdb+ is dominant everywhere on wall st, and the company mentioned in that article are retiring an old, discontinued version of k, not kdb+; perhaps that is the firm Stefan refers to? The debate about readability of k code has become boring - if you learn the language, you'll find it perfectly readable, elegant even.