Thank you for all the responses, suggestions, and lengthy discussion. Below is a summary of everything I have seen on here (per 9/12/2023)

Phased Microphone Arrays (actually used to work in this field, not discussed much, yet NASA uses these for Liftoff acoustics) - https://benwang.dev/2023/02/26/Phased-Array-Microphone.html (DIY if you'd like your own) - https://ntrs.nasa.gov/citations/20120007205 (NASA Paper)

Memristors - https://en.m.wikipedia.org/wiki/Memristor

3D Movies (has a revival almost every 20 years) - https://en.wikipedia.org/wiki/3D_film

Full Body Impermeable Swimsuits (banned after 2008 Olympics) - https://www.engineering.com/story/the-technology-behind-spee...

Mini-Disc (perhaps Multi-layer Blu Ray mini-discs?) - https://en.wikipedia.org/wiki/Blu-ray#Mini_Blu-ray_Disc

E-ink displays - https://en.wikipedia.org/wiki/E_Ink

Rear Heat Sinks for Laptops / Portables - https://www.halfbakery.com/idea/LCD_20heatsinks

CPUs in Non-standard locations (behind the screen) - https://news.ycombinator.com/item?id=37473795

Thermal Cameras - Cat S62 Pro (who knew Caterpillar had phones? Only $500 new? Yoink) - https://www.catphones.com/en-au/features/integrated-thermal-...

Alcohol Fuel Cells - https://www.renewableenergyworld.com/storage/tiny-alcohol-fu...

Personal Nuclear Systems (water heating suggested, occasionally also hear about personal nuke power in your backyard) - https://news.ycombinator.com/item?id=37473795

Automatic Food Preparer/Cooker Machines (mostly exists as restaurant automation) - https://en.wikipedia.org/wiki/Automated_restaurant

Flywheel Energy Storage (Suggestion for Sale) - https://www.torus.co/torus-flywheel

Rapid Application Development - https://en.wikipedia.org/wiki/Rapid_application_development

Ultrasonic Dishwashers (exist, just not talked about) - https://www.google.com/search?q=ultrasonic+dishwasher&source...

Ultrasonic Dishwashers (ver2, medical, really expensive, yet 0.85m x 0.85m x 1m) - https://www.proxibid.com/lotinformation/51850649/getinge-mod...

Music/mp3 Players (dedicated device, rarely mentionedd, "why not use your phone?", still exist) - https://www.google.com/search?client=firefox-b-1-d&q=dedicat...

Self-Heating Coffee/Cocoa/Ramen - https://en.wikipedia.org/wiki/Self-heating_food_packaging

Starlite Thermal Shielding Plastic (now owned by Thermashield, LLC) - https://en.m.wikipedia.org/wiki/Starlite

3D XPoint / Optane Memory (discontinued non-volatile memory, sold since 2017, largest sales non-charge storage memory) - https://en.wikipedia.org/wiki/3D_XPoint

Graphene (disagreement about my example, shrug, 150mm x 150mm for $240? 30mm x 30mm for $20? Even an 8.5 x 11 that is not) - https://news.ycombinator.com/item?id=37473795

Generalized 3D Printers (lots of varieties, just not in one machine, Note: link has slightly invasive ads) - https://all3dp.com/1/types-of-3d-printers-3d-printing-techno...

Ramjets and Scramjets - https://en.wikipedia.org/wiki/Ramjet and https://en.wikipedia.org/wiki/Scramjet

Bubble Memory (several mentions) - https://en.wikipedia.org/wiki/Bubble_memory

Hardware Accelerated 3D Sound (ex: Environmental Audio Extensions (EAX)) - https://en.wikipedia.org/wiki/Environmental_Audio_Extensions

Hydrogen Fuel Cell (not vanished, just little public awareness) -

Spatially Reconfigurable Keyboards - https://www.ergocanada.com/products/other/ergodex_dx1_input_...

Smart Dust (chips and sensors at "dust" scale) - https://en.wikipedia.org/wiki/Smartdust

General Topic Stuff:

Gartner Hype Cycle (lots of criticism, yet common, start -> hype -> disillusion -> enlighten -> productive) - https://en.wikipedia.org/wiki/Gartner_hype_cycle

Need for a market that can scale - https://news.ycombinator.com/item?id=37473795