Current market cap for BTC is ~$46Billion, which is why each BTC is ~$2.8k for it's supply. If 10% actually support BCC, the new market cap for BTC to be 41.4Bil, and be worth $2.5k/BTC?
There is no actual "Market Capitalization" for cryptocurrencies. That phrase has no real meaning when talking about a commodity or currency. It is a phrase that applies to shares of a company or business.
However, people who buy-and-sell bitcoin as a speculative investment often like to think of Bitcoin like a stock, so they multiply the current exchange rate by the total bitcoins created so far and mistakenly use the words "Market Capitalization" to describe the result.
Here's an example:
Lets say I create a brand new crypto currency. Lets say I create and give out to 1,000 people (including you) 100 DannyCoins each for free. The total number of coins created so far is 100,000. Now lets say an exchange lists my made up coin, and you list 1 DannyCoin for sale on the exchange. Lets say someone that doesn't have any DannyCoins yet buys that 1 DannyCoin from you for $50.
The total amount of fiat invested so far in DannyCoin is $50.
The market value of DannyCoin is now established at $50.
The value of your remaining 99 DannyCoins at the current market rate (for as long as $50 remains the current market value) is $4950 .
But the "so-called" Market Cap is:
$50 X 100,000 coins = $5,000,000