I don't know and i don't think that there will ever be a limit on the amount of capitalisation crypto is getting. It hasn't even been 10 years since the launch of the first crypto bitcoin and it's now a worldwide phenomenon that cannot be ignored by central bankers anymore.

It's interesting to note though that this drastic increase in market cap came at a cost - and that cost was altcoins outgrowing bitcoin significantly. I believe that this trend is ending in the near future, as altcoins will generally die off in interest periodically but bitcoin has a sustained interest.

And plus - fiat can go from real value to nothingness in a year. We never know, we might not even measure market cap in terms of fiat anymore.