Ok, let's assume that the OP made a mistake which it will probably $1.4T.
My opinion about $1.4T market cap of cryptocurrency is really POSSIBLE. Especially when Bitcoin will break the previous ALL-TIME HIGH which is around $19,000.

Especially when the price of Bitcoin reached around $19,000 before, the market cap is around already $700,000,000. So, let's say that the price of Bitcoin will reach double the ALL-TIME HIGH price, around $40,000 per Bitcoin.
Then it is really possible, especially there will be some altcoins will gain huge market cap. Altcoins will also help the market cap of cryptocurrencies soar, even the Bitcoin dominance is surging up.