The Wikipedia article is misleading. SIS was not Shimano's first indexed system. That honour belongs to 1975 Positron which was intended for low end models and was the first indexed derailleur system to achieve significant market share. It was followed in 1981 by New Positive Mechanism, which was simultaneously introduced on four different AX groups. SIS was an evolutionary change that would eventually lead to STI (Shimano Total Integration, generically known as brifters). However, SIS was historically significant in that it triggered the industry wide shift to indexed shift systems, with SunTour and Campagnolo quickly responding with their respective introductions of AccuShift and Syncro .

Also, while Shimano changed their marketing approach with the introduction of SIS, by introducing it on their top road group and then trickling it down the line, it had nothing to do with proving the product and customer acceptance. SIS was commercially introduced in the autumn of 1984 for the 1985 model year on New Dura-Ace (7400 series). It had already been thoroughly tested in professional racing during the 1984 season, notably with Urs Zimmermann using it to win the 1984 Tour de Suisse for the Cilo-Aufina team. Between that and in-house accelerated testing, Shimano already had the feedback on performance.

Regarding consumer acceptance, that was a calculated risk that Shimano was willing to take. SIS was trickled down to New 600EX and LIght Action in the autumn of 1985, for the 1986 model year. Production of these shift systems would already have started by mid-1985, before Shimano had much consumer feedback on SIS from New Dura-Ace. Furthermore, the 1987 model year groups receiving SIS (Santé, New 105, Deore XT and New Deore) were probably already on the drawing board before Shimano got any useful amount of consumer feedback. The circumstantial evidence suggests that Shimano was committed to SIS and quickly trickling it down through the majority of the product line, whether or not there was customer acceptance.