I don't know that being schemaless is fundamentally different. Instead of thinking that key/value stores are schemaless, I think of them as having a single rigid schema: key and value. The data you stick into a k/v db will still have essentially, a schema, you just end up writing your application to be flexible to data inconsistency.
The comparison to dynamic vs static typing doesn't hold much water.
Can you explain how meta-programming relates to this topic at all?
Metaprogramming: I think he/she is associating schema-less DBs with dynamically typed languages and metaprogramming, and static typing with languages such as C that tend to lack sophisticated metaprogramming facilities.
I'm not sure it's a valid comparison, though: OCaml has a statically typed Lisp-style macro engine (camlp4), for example. (In all honesty, though, I've never used it. Lazy evaluation, the packaging system, and other language features cover many of the same use cases.) I think it's a case of assuming the C family's type system is the cutting edge of static typing, when it's actually pretty archaic.
The point about K/V databases having a rigid schema of (key_type -> untyped_value) is a good one, by the way. Of course, association tables (AKA "dictionaries") are pretty versatile as a basic collection type - looking at Lua, Python, Awk, or Javascript. They're not ideal for all cases, but they're a good start for most.
Sure I can see the single rigid schema view. But I'd rather see the K/V as just a persistence mechanism. I view the schema as being more related to the application.
meta-programming relationship:
Since you can store anything in the value part of a K/V store. You could (and I do) store the schema definitions for the other values in the data store. And while you are at it, you could store code segments.
So imagine the following key store (in pseudo code):
You could stuff code segments in there in a similar way. So I think K/V stores are potentially highly related to meta-programming. Though certainly the two could exist entirely separately of each other.
The comparison to dynamic vs static typing doesn't hold much water.
Can you explain how meta-programming relates to this topic at all?