Changing the vernacular would only change the vernacular not produce any type of intellectual increase. There have always been less intelligent people. People we would consider dumb or stupid but their choice of words varies depending on the vocabulary of the culture they're from. An example of this would be letters from soldiers of the civil war era versus letters from soldiers now. They weren't necessarily any smarter or are we any dumber we just use different words. Here's an example of a bygone era: dp . la/primary-source-sets/battle-of-gettysburg/sources/1469
Which is a good thing, but not a realistic expectation. On average we only use around 2k-3k words in normal conversations. That's not much when you consider that English contains 50000+ words. However it is not just English that that average holds true. In every spoken language regardless of the size normal conversations only use 2k-3k words. So introducing new vocabulary isn't going to change those numbers unless you also increase the verbosity of average conversations. This would have the effect of keeping the current vernacular and introducing more words and then utilizing both. Problem is you're never going to convince people to keep using their current words and the new ones. The more effective method would be to require everyone to read a certain number of books every year in school, with accompanying tests or reports, and increasing the reading level and number of books every year. This would achieve the results I think they're looking for.
But how?