"New Twitter" is basically just the mobile site becoming the only site, isn't it? I feel like this is something that was reported as coming months ago, but that may be something I knew only from being soaked in tech nerdery.
@floatoverblow it's possible that there just aren't many people using it on the desktop and they didn't feel like maintaining two web versions anymore. They killed the official desktop Mac app years ago, along with Tweetdeck apps. (Which wouldn't bother me as much if they hadn't also deliberately broken the API for third-party clients, but, well.)