The notion of altcoin will not exist any more. Bitcoin will have become a coin like any other.
First mover advantage gone if ever that happens.
Wrong. BTU will be, per definition, an altcoin. I'm not going to comment the latter part, but it will surely have a negative effect short term. I guess this is what they wanted when they were "concerned with the user experience".

These you have it folks, the economic majority is coming to a consensus that the BU implementation is an altcoin and will be listed under BTU.

But won't BU still make bitcoin's price go down a bunch, if it hardforks?
I'm a bit confused of this whole situation. I tried reading about this in many different places, such as coinbase, and everyone keeps saying bitcoin will hardfork. That would then decrease the value of bitcoin?? I'm a bit scared of what will happen with bitcoin to be honest.
Yes; to be frank, it will be a "fucking blood bath". Whales supporting their own chain will be dumping the other chain to the ground in hopes that their chain is significantly stronger than the opposition.