Isn't MicroSD what you want? Even when hard discs were tiny they were bigger than any floppies. Zip drives were possibly the closest, but they were only used because they were portable, not because they were any good.

Zip drives could also go bad and screw up your data if the mechanism failed. Stupid click of death... a completely separate storage layer can't always save you.

Well the problem there was that, iirc, they had the RW mechanics alongside the platter. Thus they got bumped around during transport.

Without that the damage would have been piecemeal as sectors went bad, rather than watching a chip go poof and lose access to everything.

SDs still have a level of electronics between the storage IC and the rest of the system. There may have been a solid state format like what i'm thinking about, but i think it is long defunct.

What's wrong with BD-R?

Can't really be used in a "drag and drop" fashion.

Wasn't DVD-RAM meant to work for that? Did anyone ever use it?

There was/is a packet writing format that can be used, as far back as CD-R i think, but early Windows needed a special driver just to read them. Supposedly Universal Disk Format (UDF, DVD and later) has it baked in. But i can't say i have ever seen it used.