Do you think there could be anything other than Bitcoin in terms of long-term planning?
In Crypto currency world I don't think that there is any others better options like bitcoin . Because Bitcoin is perfect for both security plus profit. Bitcoin is one of the best digital assets. So there will be no question of how Bitcoin will be for the long-term, practically if we look at the previous history it will definitely be good. But since you have mentioned trading pairs here, I would say that selection of trading pairs really depends on personal strategy. It can be different for everyone on those uses
That's the thing which makes the pair better, people love bitcoin and you may disagree on some other coins together, not everyone will agree that some altcoin could be good, but everyone agrees that bitcoin is great and that makes it so much fun.
I personally would love to get as much bitcoin as possible, but if I had another altcoin, I may sell some of it to get bitcoin instead. Think about it, if you give me a million dollars worth of even ETH (and certainly all other coins) I would still sell some of that and buy bitcoin, but if you gave me a million dollars worth of bitcoin, I may keep that. This makes the bitcoin trading pair as the best one against any coin out there in the world and that is why people prefer it.