My personal opinion, with influence from Martin's comments on previous tag-related things: I don't see vimscript lambdas being a high-signal technical subject in which you can have expertise, and I find it unlikely that people are trying to connect to questions specifically about vimscript lambdas.
From a community perspective: if people want the tag, so it shall be :)
A technical nit: "lambda" is not the name for a function that can be "passed around." There are lots of concepts at play here:
- A "lambda" is a (syntactic) expression whose value is a function, sometimes called a closure when it also creates a lexical (or dynamic) closure, which most do.
- A language has "first-class functions" when a function is a valid kind of value, for example, when it is possible to construct functions and pass them as arguments.
- First-class functions are used by most kinds of functional programming, as noted, usually as arguments to higher-order functions. These arguments need not be lambdas (if the language supports proper first-class functions). Other kinds of syntactic expressions can evaluate to functions; lambdas are but one kind.