Source engine is so outdated at this point anyways. Valve should use the profits from their cash cow, CSGO, and use it to invest in retooling with open source engines such as GoDot or Bevy.

I remember downloading a leaked version of the source code for source engine, and in general it was laughable at how awful it was. I dont know if it was ever discussed mainstream but only based on recollection of IRC chats.

I think it was about 6 months out of date, but even so it would explain why HL sequels would become vaporware despite years of teasing the community by Gabe Newell himself.