Traditionally, anything above ~350% has indicated a bubble. With the housing bubble, we saw a peak of 473%, and the dot-com bubble was 429% at its peak. Essentially, yes, wealth will be a multiple of GDP, but the multiple has been fairly constant historically, and it's diverging rapidly now. So either we're in an era where assets are significantly more valuable (and I'm not sure there's a good case for that given the multiplier), or we're in an asset bubble.