The phrase "a mainstream idea" is correct and usable in written English.
You can use it to refer to an idea that is widely accepted or popular among the general public or within a particular field.
Example: "The concept of renewable energy has become a mainstream idea in discussions about climate change and sustainability."
Alternatives: "a popular notion" or "a widely accepted concept."
Sustainability — a notion mostly heard in environmental circles only a decade ago — has become a mainstream idea to which some companies are committed and many are paying lip service.
"It is still not a mainstream idea – we are still a minority," Leung admitted.
What started as a fad for idealists has now become a mainstream idea debated by pension-fund trustees, fund managers and company executives.Many remain sceptical about so-called socially responsible investment (SRI).
"It's now a mainstream idea that no one should be allowed to tell us that we need to diet in order to have worth in this world," Ms. Leive said, "and it wasn't 10 years ago".
Glass, the hi-tech spectacles launched by Google in 2014, were an AR device, but the company has given up on trying to sell them as a mainstream idea.
It is a shame — though not coincidental — that just as universal health care is becoming a mainstream idea and "Medicare for all" is gaining currency as a solution, there is a rush to privatization and profit-making.
The people were for such a change, which only goes to prove that it wasn't some fringe "lefty" idea, but in fact a very mainstream idea that a large majority of the public supported.
"It's no longer a wacky idea cloistered in the ivory tower; it's become a more mainstream idea that we need a different kind of copyright regime to support the wide range of activities in cyberspace".
She actually has a mildly mainstream idea working with the documentary part of the movie.
This is dismaying but it is important to understand that a fundamental mainstream idea was behind it.
"ChimaTEK™ is the technology that the Empathics have produced to try and create a more mainstream idea of what the Institute of Empathy's research can actually do.
