This idea will never become a reality for the vast majority of companies, for the exact same reason that companies fear piracy. If I open source my product then anyone who uses that open source code is a lost sale. A lost sale means I make less money, less money means the board is mad, on and on and on...
The bottom line is money, and open sourcing their code means (to them) a loss in potential revenue.
I predict the open source bits will be bait. With many 90% solutions. The proprietary bits will be the ones you need to make it work like a real program. Oh there will still be soup to nuts full on free stacks. But I seeing more and more of this service fee way.
As for making hiring easier? Not so much. When you can get 100+ applicants for 1 position. The reality is at least 99 of those have to go away. One more filter does not do much other than let you round bin things faster say 'cant find anyone' then grab your favorite contracting firm and hire them anyway.
But I went from needing technical support from elastic 4-5 times a year, to zero and found work arounds for the other limitations, like cognito for authorization and storing less data in the cluster. The end result was a six-figure savings on licensing and less weekend work for me at the cost of a five-figure increase in AWS costs.
I'd say it was worth it.
I doubt proprietary tech is going to fade completely, but it's true that maybe there are forces that are pushing for big companies to make more and more projects open source. If you think about it it makes sense: the employees are happier because their work has more impact, they also benefit because they can showcase it in their CV. For the company they externalize testing, quality improves because employees are going to be more careful when their code is in the open and they are more motivated. It can also make hiring easier.