Unlike most other high-end series, there is little to say about the eXclusive series : no botched marketing, no conflicting lineups, no crazy technologies, no nonsense.
The only thing one could argue about is that, apart from the first two components, distribution was limited to Japan - exclusive indeed but a bit conservative, especially considering the strength of the brand in the USA, Germany and Italy...
Pioneer somewhat corrected that with the very successful SPEC-1, SPEC-2, SPEC-3 and SPEC-4, respectively C-77 / M-77 and C-73 / M-73 in Japan.
The eXclusive series, however, started with two components which did not bear the name - that's very Supreme, very ESOTEC, very ES or pre-Esprit :)
The SC-100 and SM-100 were launched way back in 1967, after which several updated versions were produced (SC/SM-3000, SC/SM-300) before eXclusive at last came to be, early in 1973 : Exclusive C3 and Exclusive M3.
New components and updated versions were launched gradually, slowly, often very slowly, but with constant success and sales throughout the 1970s and speakers shared between the TAD (pro) lineups and the eXclusive (consumer) series.
The early 1980s saw Pioneer work slower on the series, busy as it were becoming an industry major with car-audio and Laserdisc, and that's when sales somewhat stalled.
The eXclusive series didn't cater to trends, whether technical or visual, and, by 1982, they all looked very 70s-ish : big luxurious boxes of metal and wood with plenty of knobs and old-fashioned needle VU meters. Although Pioneer planned very "modern" designs as early as 1973, these never came to be and the modernistic look befell the Z1 series.
So the 1980s saw only two new developments (M5 & C5) and two members of the series updated (P3a & M5a / M6) until full replacements were developed for the upcoming decade : enter the ultimate C7, M7, V7 and M8.
The former two sold fairly well (considering the list prices) and were even somewhat distributed outside Japan.
But after that... nothing : the 1990 financial bubble bursting and the 1980s gradual "invasion" of EU and US brands such as Mark Levinson or Threshold made the japanese high-end go bust.
Speakers excepted, the eXclusives chronologically appeared as follows :
C3 & M3
P3 & P10
C3a & M4a
C10 & M10
M5a & M6
M7 & V7
All other brands have long since stopped the support of whatever high-end they did produce throughout the 1970s and 1980s (Kenwood, Sony, Yamaha, Onkyo, Denon et al), but as of 2013 Pioneer in Japan still has an outfit dedicated solely to the servicing of all eXclusives (plus the Z1s and high-end LD / MUSE players) - I don't know how long it will last.
But there is one thing worth noting, one that is very not Pioneer at all : all corporate and consumer sources give completely different release dates for each component produced since 1973. As if the production and release of the components had happened out of time, out of any schedule or precise red tape.
But then, the eXclusive series was indeed engineered and produced as such : above and over time, trends and marketing necessities.
In a word : timeless.