https://en.wikipedia.org/wiki/D-VHS
about a decade after that someone asked me for help reading a crate of these tapes that had been flooded then stored in a shed for several years. Couldn't help them at all but it was an amusing diversion figuring out what the hell they had.
https://www.youtube.com/watch?v=papQ8xQxizA
When I was at LSI Logic, I developed the IEEE1394 interface for the second generation JVC D-VHS decks (the HM-DH40000U and HM-DH5U). I worked directly with engineers in Japan and I used to get them to bring me copies of the Japanese ham radio magazine "CQ ham radio" when they would come to visit us in Milpitas. I can't read Japanese, but it's just a wonderful magazine about 300 pages thick (like the old Byte magazine).
When I was hunting information for that client; I found a deck and interface card on ebay for some fairly trivial amount, $200 or so. I was really tempted to grab it just for the "neat weird gear" pile but couldn't justify it. The tapes they wanted read had been submerged for some days and were crusty. The media might have been recoverable but it would have meant pulling it out and putting the tape into new cartridges.
Am I correct in remembering that standard VHS tapes were usable in these drives?
I had no practical use for them as my family didn't have an HDTV for a few more years, nor lived in an country where 1394 was enabled by default on cable boxes. However, the very idea of having a MPEG TS captured on a commodity tape was alluring in being able to have a perfect copy of whatever was on TV.
Alesis also developed an 8-track digital audio recorder based on VHS, ADAT, which used SVHS tapes and could record 20-bit 48khz. ADAT was pretty popular in smaller studios, and was great for the time before multi-gigabyte hard drives. https://en.wikipedia.org/wiki/ADAT
OP's project is cool but it's my understanding the specialized hardware is the big barrier to doing this at home, for most folks, especially if you don't want the tapes routed through a third party for the same reason people invented the polaroid so you don't have to send everything to the Ritz as the mall.
And - if I remember correcly - GRAU and/or StorageTek robotic tape libraries also had support for VHS devices.
Only the tape drives are extremely expensive (thousands of $).
If you have hundreds of TB of data, LTO, including the cost of the drive, becomes cheaper than HDDs.
The QIC tape cartridges had the problem that the rubber belt which moves the tape disintegrates after a number of years, making them unreadable without special equipment.
The LTO tapes have a much longer lifetime.