Feature creep
The phrase feature creep dates to at least 1990, as used in a comp.sys.mac Usenet post on the San Francisco MacWorld Expo of April 15, 1990:
As an industry 'matures' everyone starts to look
the same and the shows
get less interesting, fewer and fewer really
wonderfully new and
striking products (I think it's because all the
relatively obvious stuff gets done). Everyone ends up playing 'feature creep' with their competitors.
Three months later in the same group, a reply to a "Finder 7.0 suggestion" on July 13, 1990:
There's really no need for something that specific:
System 7.0's
InterApplication Communication model already
provides a foundation for
doing this sort of thing. ... Apple hasn't actually
designed a stream Manager with the functions that you describe,
probably because they
wanted to leave something for the developers to
do. I also suspect
that Apple System Software Engineers probably
have better things to worry about than standardizing a Spelling
dictionary. In a previous
message, somebody mentioned Feature Creep, and I think it applies very
well.
By 1993, it was more common in Usenet.
Creeping featurism
The earlier phrase creeping featurism shows up in Jargon File 1.1.3 (dated 22nd July 1981) as a form of soundalike slang:
creeping featurism => feeping creaturism
Feature creep itself doesn't show up until Jargon File 4.1.0 (dated 12th March 1999):
:feature creep: n. The result of {creeping featurism}, as in
"Emacs has a bad case of feature creep".
Requirements creep
The synonymous feature creep shows up in snippets of the Department of Defense Authorization for Appropriations for Fiscal Year 1985, published in 1984:
Experience has shown that longer production runs result in requirements "creep". To improve this estimate for budgetary purposes would require the Air Force to formally task the contractors to provide cost estimates detail keyed to a hypothetical production rate.
The following year, a snippet of Department of Defense appropriations for 1986: hearings before a subcommittee of the Committee on Appropriations, House of Representatives, Ninety-ninth Congress, first session, Part 2 says:
We have put a very solid reign on gold-plating, on requirements creep, and on engineering change orders. Everything that has any impact on the cost of a contract once signed, must be approved for a waiver by the CNO, by me or the Commandant if it is a Marine program.
In 1986 it shows up in IEEE documents about avionics, and in 1987 IEEE conference records, and from there into other software engineering books.
Mission creep
Feature creep probably isn't derived from mission creep, defined by the Oxford English Dictionary as:
orig. U.S. Mil. slang a gradual
shift in political or strategic objectives during the
course of a military campaign, frequently
resulting in an unresolved conflict or open-ended
commitment; also in extended use.
Their first citation is from 1991:
We're going into a conflict with an ill-defined
mission, there is mission creep in a much more
compressed time frame, [etc.].
The earliest I found is in the Los Angeles Times of Sunday, June 27, 1993 ("Soldiers of the New World Order - Aggressive Peacemakers, U.S. Marines Draw Down the Warlords of Somalia and Write a Military Blueprint for Future Campaigns"):
But Abbot never did just the minimum in Somalia; he was singled out, in fact, by Gen. Johnston as one of the commanders who went beyond the Marines' primary mission of securing food-supply routes and neutralizing Somalia's warring clans and bandits--a task accomplished within two months of the Marines' arrival--into such development projects as rebuilding local police departments, schools and community centers. Johnston called it "Mission Creep."
Other creep
Here's a 1960 "nucleur creep" and a 1983 "speciality creep", both from Military Review.