If the Bundesliga continues to play on a very high level teams like Schalke, Hamburg, Frankfurt or Gladbach will attract fans all over the world again.
No, they will not. Just as Leverkusen didn't after playing CL final.
Chelsea are popular because they continuously have one of best world's squads and will continue to have it under Abramovich. City just started to do the same.
City, Tottenham, Everton etc. will always trigger interest as they are on one or another way the rivals to some of world's most popular football clubs and they all together are rivals to extremely popular club Rags are. City would never have success marketing and growth wise as it did and as it will without being rags city rivals. That's why ADUG picked it and that's why they were exploring option to buy Everton.
That level of rivalry and competition will never happen at Bundesliga as Bayern are and always will be miles in front of their competition and current Bundesliga ownership regulative is taking care that it won't change ever.
Playing good football, having full stadiums, performing well in Europa League is not what rises popularity. Just as having beautiful voice alone won't make you to hit top of charts. There is that "something else" that's needed and Bundesliga just don't have that "something else" compared to Premier League and are too, too late in their attempts to challenge it.
As someone else noted before, another advantage of Premier League is language. English is widely spoken all over the world and fans are able to follow news from original sources much easier than with German ones and that continuous connection is something that make you more and more connected..