The worst case for Bitcoin is probably the rapid development of other coins, Bitcoin cannot keep up, so bitcoin prices cannot increase but continually decrease.
Even though there is rapid development with the Bitcoin, there is less possibility for other coins to have a community like Bitcoin. Bitcoin is always the dominant currency because the majority of the investors still have high hopes of Bitcoin compared to others because other coins price is dropping very hugely.
yes, obviously bitcoin has been widely trusted by investors in this field, even though there are always new types of coins popping up if coins cannot be converted to bitcoin, newly launched coins will not be worth even their growth will not last long.