- Plated through hole edge connector proto board for an economical price. (I may just end up having this manufactured. Vectorboard Plugbords cost at least 25 dollars each, but the cheapest fabs I know of will make them in quantity 100 for under 5 dollars a board, I think.)
- Cheap tightly regulated 24 volt DC/DC supplies with 10 kV isolation. Something with some of those features exists, just not all of them. Have actually ended up deciding to buy stacks of cheap DIN rail supplies, which have 3 kV isolation, instead. May end up going to 60 Hertz Hell.
- <10 femtoampere leakage current gas discharge tube voltage limiters
- 1 kilovolt high speed (but stable at unity gain and DC) op-amps.
- Actually good high-current-output op-amps
- Cortex M4F microcontroller, in DIP package, with built in USB and JTAG, and with minimal GPIO but a high-speed/high-bandwidth/moderate-distance bus (multiple lines of high-speed RS485 maybe?), and the ability to connect to arbitrary IO modules also in DIP package (UART, SPI ,I2C, GPIO, 8-bit sub-processor, small patch of FPGA fabric, etc). Kinda like a modular PLC, but for much lower-level software and hardware.
- Single chip, non-tiny-package, military temperature range multi-cell complete Li-ion charger/controller unit that handles the complete combo of: Cell protection, high speed charging, trickle (solar) charging, gas gauging, and output disconnect. I am amazed that Sparkfun does not sell any such device.
- Automagical tri-state bidirectional output buffer / input limiter / level shifter / isolator pack.
- Lithium battery packs with similar market penetration to the AA battery
- A truly rail-to-rail op-amp (maybe with internal charge pump...)
- Spray-on IP65 Rating for switches and connectors
- Ceramic or PEEK UHV compatible Mini DIN connectors. (Something similar does exist, the "Sub-C" connector, but very expensive, overly complicated w/ crimp pins, and rather bulky.)
- Peltier modules with efficiency befitting a solid-state device.
- MLC protoboard
- A material that has the consistency of modelling clay when supplied but hardens into a polymer with temperature and outgassing properties similar to PEEK. (I made something like this by mixing Loctite/Hysol 1C epoxy with powdered plaster-like ceramic potting compound. It kinda worked.)
- Room Temperature Vulcanizing Viton rubber
- Paint-on / Dip-on Thermionic Cathode Coating. I know that something approaching this existed in the heyday of vacuum tubes, but supposedly it didn't work very well.