That just opens another can of worms. Now every single application you either provide or use come with an integration issue attached.

I have read somewhere that was the Amazon way of doing thing but it was a costly investment. A costly technological investment. And even Amazon did it only at team level, not individual level.

I cannot imagine a 500 developers company being able to afford that without some serious competitive advantages down the line. If what I can see around here is any indication (medium size IT company in London), if you can afford not having people on site, there are better opportunities to take in Poland or even India than a small discount on a UK worker.

Unfortunately, a network API letting you mix and match languages still opens up risk from a rogue employee who uses something different than the status quo and then quits, leaving something unfamiliar that needs to be maintained.