I'm not so sure.
The Premier League is clearly the most successful league in football, and six rich teams is probably enough to sustain things. It's not popular because Villa or Everton might make a run into the top four once a decade.
There's no major reason why United and Chelsea shouldn't be able to challenge again, given their current financial size. Spurs new stadium has pushed their revenue up massively, and we've seen that Arsenal are again able to compete. With a fifth CL spot it'll be even easier for the rich six to sustain.
The six gives some semblance of competition, and it's certainly more than any of the other big leagues. People always used to talk about cycles, but the financial gaps have become so great, that I don't see how other European leagues could catch up, and if the PL remains the most popular, then the money continues to flow in.