Well, the Welsh example is exactly what I'm talking about. The government took giant leaps to preserve the Welsh language, because it would've died out if it hadn't. People always pick the easiest solution, generally.
But the Dutch situation is a bit different than the Belgian. Frisian is still spoken, yes, but that doesn't mean you're required to know it if you live in the Netherlands (as far as I recall). If you're Belgian, you're pretty much required to be bilingual (Dutch/French) for just about any jobs, at least in Flanders. On top of that, you should have a basic understanding of the German language as well, as it's also an official Belgian language. Linguistically speaking, I think giving back the German part (which we stole from Germany after WWI IIRC), adding Flanders to the Netherlands (or making an autonomous region if no consensus can be made), and adding Wallonia to France, would make everything so much simpler. Because if there is only one dominant native tongue, adding a second universal language is quite doable.
But if we treat this 'universal language' as just another addition to take or leave, it's never going to be universal. I am actually amazed daily at the inability of most to spell and phrase certain simple sentences in English. It's a language we all know from tv and internet, but it's nowhere near a real spoken tongue here.