False premise request

MYTH came to my mind, although it might not fit your case.

From dictionary.com:

An unproved or false collective belief that is used to justify a social institution

The best word that I can think of to describe the request is "pitfall."

From Merriam-Webster:

a hidden or not easily recognized danger or difficulty

I am a software developer myself so I get these kinds of requests from clients all the time. From the perspective of the client the feature request is perfectly rational. It is only you, the professional software developer, that can spot the hidden danger in implementing such a request.

The examples may be instances of ignoratio elenchi, that is to say, irrelevant conclusion or irrelevant thesis informal fallacies.

Informally and less specifically, one could refer to faulty reasoning, being over-hasty, jumping to conclusions, or making premature judgements. The examples also can be said to ignore the design principle of least surprise (or least astonishment).

Such requests or requirements reveal themselves to be impracticable or unfeasible.

You can say that the idea turned out to be a blind alley:

Blind alleys and garden paths leading nowhere are the principal hazards in research. [Lewis Thomas]