Predatory Cryptocurrencies

[spcrypto]

Hello, I have been mining cryptocurrencies on my desktop computer for about month now and have a few miscellaneous questions that I have not been able to find the answer to.  Here is one theoretical question I have.

What kind of threat do cryptocurrencies pose to one another?  Could a cryptocurrency use its miners to hijack another cryptocurrency without compromising its own security?  Here is the simplest example I can think of that might do this.

Let’s assume a new cryptocurrency named Gazelle Coin is released into the wild and receives a modest reception from the public.  Shortly after its release a variant of Gazelle Coin named Lion Coin is released.  Lion Coin uses the same rules for its ledger as Gazelle Coin, but has some arbitrary additional rule (perhaps public keys cannot start with a certain character).  This makes Lion Coin’s ledger compatible with Gazelle Coin’s, but Gazelle Coin’s ledger is incompatible with Lion Coin’s.  In addition Lion Coin broadcasts its ledger as both a Lion Coin ledger and a Gazelle Coin ledger.

Since Lion Coin was released after Gazelle Coin, its block chain starts off smaller than Gazelle Coin, so broadcasting its ledger has no initial effect on Gazelle Coin.   As Lion Coin grows in popularity its block chain eventually becomes longer than Gazelle Coin and Gazelle Coin automatically adopts the new longer block chain.  This shifts ownership of Gazelle Coins from their previous owners to the owners of Lion Coins.

Is this scenario realistic?  If not, what would prevent this from happening?