J.E. Lighter, Random House Historical Dictionary of American Slang, volume 2 (1997) has an on-point entry for Mc- as used in the relevant sense:
Mc- prefix. {fr. McDonald's, international chain of uniform fast-food restaurants} Orig[inally] Stu[dent use] (used to emphasize the generic nature, mediocre quality, commercialization, or mass-market appeal of the following noun).—used derisively. Joc[ular]. See also [the entry for] McJob.{Discussed with extensive citations fr. 1986–88 in G Lentine and R.W. Shuy, "Mc-: Meaning in the Marketplace," A[merican] S[peech] LXV (1990), pp. 349–66.}
[First five cited examples:] 1984 Mason & Rheingold Slanguage: Mcmoon {"moon"}. 1985 Wash. Post (Apr. 13) 12, in Barnhart Dict. Comp. IV.4 ((Winter 1985) 138: "Surgicenters" and "quick care centers" that have sprung up in business districts and shopping centers. There are 2,500 such mini-clinics—sometimes dubbed "McDoctors"—today. 1986 in A[merican] S[peech] LXV (1990) 364: Three "McReads" just right for an airport layover. 1989 P. Munro U.C.L.A. Sl[ang]: MPaper poor, hurriedly written paper done without much research or forethought. 1990 New Republic (May 21) 28: The homogenization of the non-profit stage. I call this process "McTheater."
Site participants who are interested in the Winter 1990 American Speech article by Genine Lentine and Roger Shuy that Lighter cites and who have tie-ins to universities can find the article at JSTOR; as a nonscholar, I don't have access to it through this portal.
Somewhat surprisingly, although Lighter also lists instances of "McNews" and "McStar" (both from 1991); "McSchool," "McGuggenheim," "McAlternatives," and "McPublishers" (all from 1992); "McFirm" (from 1993); "McSex" (from (1995), and "McWifes and McJobs" (from 1997), it doesn't cover the very widespread term "McMansion." The earliest instance of "McMansion" that I've been able to find is from Joni Hilton, Braces, Gym Suits, and Early-morning Seminary: A Youthquake Survival Manual (1985), where it seems to refer not to a generic style of structure but to the pet name of particular building—like "McTara" or "McManderley." Use of "McMansion" in a generic sense seems to have become widespread in the early 1990s.
In any case, Lighter's description of "Mc-" as a prefix "used to emphasize the generic nature, mediocre quality, commercialization, or mass-market appeal of the following noun" can scarcely be improved on. Nor is there any doubt in Lighter's mind that the inspiration for this use of "Mc-" is Ray Kroc's low-end conveyor-belt fast-food empire, not a Monty Python skit. I concur with him wholeheartedly.