The Jargon File (version 4.4.7, 29 Dec 2003):

heatseeker
 n.

    [IBM] A customer who can be relied upon to buy, without fail, the latest
    version of an existing product (not quite the same as a member of the 
    lunatic fringe). A 1993 example of a heatseeker was someone who, owning a
    286 PC and Windows 3.0, went out and bought Windows 3.1 (which offers no
    worthwhile benefits unless you have a 386). If all customers were
    heatseekers, vast amounts of money could be made by just fixing some of the
    bugs in each release (n) and selling it to them as release (n+1). Microsoft
    in fact seems to have mastered this technique.


The Free On-line Dictionary of Computing (30 December 2018):

heatseeker

    (IBM) A customer who can be relied upon to
   buy, without fail, the latest version of an existing product
   (not quite the same as a member of the lunatic fringe).  A
   1993 example of a heatseeker is someone who, owning a 286 PC
   and Windows 3.0, goes out and buys Windows 3.1 (which offers
   no worthwhile benefits unless you have a 386).  If all
   customers were heatseekers, vast amounts of money could be
   made by just fixing the bugs in each release (n) and selling
   it to them as release (n+1).

   [Jargon File]

   (1996-03-12)