It will give me hope if this flops, because maybe then the reason people stay with Twitter is the network effect, and not anything actually to do with its rancid owner.
Video hosting in general is not profitable, this is almost certainly not gonna do anything to help Twitter survive, hopefully they'll shoot themselves in foot even more.
Why would this increase costs? I doubt Elon Musk is spending much money on the development of this, and I don't see many people using this app so I doubt it'd hike hosting and bandwidth demands significantly.
It sounds like a YouTube clone from the article, so long form videos storage and streaming isn't cheap, a lot more expensive than what x usually hosts in terms of bandwidth and storage per views. But yeah also seems like a niche use case.
Still no way there's a net cost benefit to video hosting from as revenue.