Wow wow wow. What an incredible game. Where do I even begin. The vibe of the game was amazing. Your work with shaders, UI design, and gameplay elements was AA or AAA worthy. You could totally create or sell assets or courses for other people to use or learn from respectively. I know I could learn a lot!
The gameplay loop itself was fun. Speed D1ff draws a lot of similarities from a game like Paper's Please, where speed and careful consideration of detail clash with one another, stressing out the player.
I didn't have an opportunity to try the ONL1NE shift but I totally see the appeal. This would be a fun party game to play for a few hours.
I really like how the game asks you to lean forward to increase productivity, despite making the task-at-hand more difficult by requiring you to use peripheral vision in a wide cone, rather than having a focused FOV over all elements on the screen at once. After leaning back, the game became much easier.
You should use this terminal, the mechanics, the UI, and the sound design in a horror game. Perhaps a FNAF-Style game? The nature of the tasks you've created requires a lot of focus. This could clash nicely with the multitasking that's required out of a FNAF-style game. Same with the audio design you've created. The retro noises and ambient droning of the computer will clash extremely loud with the eerie silence and subtle sound cues of something creeping around you. I could see a dynamic where, at one moment you're working on your computer, then you hear what you think is a quiet sound cue. You shut off your computer and its fan whirs down. Your eyes slowly adjust to the sudden darkness and you focus on the misplaced silence.
Chills.
For future games, I did experience what I'd consider to be a slightly annoying but. Hitting Escape seems to be the only way to leave the inbox screen, but doing so un-fullscreens the game due to how web embeds work on Firefox. Maybe for the future, use the 'Q' key to quit? Just a thought!