Format obsolescence is an issue with ALL new technologies. The binder stability problem can be overcome, to some degree, by storing the tapes at 25 percent RH and at a temperature below 70 F. Some of the tape manufacturers now make products with a reasonable long-life binder but you have to ask them which tapes are archival. Format obsolescence is not as bad as some people claim. Yes, it would be expensive, but doable. That's why I do not recommend non standard formats for archival material.
Compression is another issue.
Formats that use compression should not be used as an archival medium. I hope you realize that this makes clay and stone look appealing. You make a good point about access vs preservation. Archives must make the material accessible To me, S-VHS is a good access format and it will be for many years. The Email You Want.