Interesting speculation, but still on quite thin ice as we all know CoinMarketCap until recently had quite strict limitations on listed coins, so it barely contains small fraction of available cryptocurrencies...
It is true that exchange rate of individual cryptocurrencies would sky rocket if someone would try to buy large amount of coins in short period of time, but it could also mean that other "sleeping" buyers would try to block the trade by creating more orders just above the price the large buyer is prepared to pay.
In the end the takeover could fail due to too many new investors entering the market and repeatedly increasing the exchange rate until the exchange would crash or freeze under stress. We all know the Slashdot effect...
Of all the cryptocurrencies on exchanges, I believe coinmarketcap has just about all of them, no?
Like I said CMC didn't previously accept cryptocurrencies with relatively low trading volume. After their policy change, cryptocurrency developers have to explicitly ask CMC to review their coin before it is added to CMC.