Newton Storage History (2007)
dadhacker.com
dadhacker.com
I think that systems like ReThinkDB are really close, if not superior. One thing the Newt never had to worry about was concurrency; the scripting environment was single-threaded, and the storage system only ever had one transaction at a time (with some advanced cheating going on for background storage operations and garbage collection). Modern systems solve harder problems, albeit with many orders of magnitude more resources and way better tools.
CouchDB is pretty close in principle but does a lot more stuff. For something closer to the original, I think you could do it PostgreSQL quite easily. But then you need a language layer...I think ECMAScript proxies might work. Hmm, I guess somebody should make an npm module!
I tended to view Palm programming as an exercise in writing C code that had be written with the intervening 20 years of aggregate experience on good design.
In the modern era of sandboxing, this is impossible, and services don't compose nearly so well.