First, I really do not want to derail this nice thread, which is certainly not about Apple, but I think there are more general aspects to this, as well. Namely, aspects of thermal design.
So there is this narrative about Jobs maliciously crippling the IIGS to protect his own baby, the Mac. However, we may also consider the very situation Apple was in at that time: Apple had just gone from one of the fastest growing companies to the brink of bankruptcy thanks to the thermal disaster that was the Apple III with its warping board and the subsequent recalls. At that time, Apple had a quite extensive line-up, with various flavors of the Apple ][, the high-end business package that was the Lisa (which was actually performing better than the marketing forecasts), the Mac, the ill-fated Apple III (as Apple’s future in the education market and in the low-end business segment), and the new machine (which was at that time reported as a possible, somewhat cubic shaped Apple IV) in the making. With the financial strain put on the company by the Apple III disaster, Apple had to radically reduce the line-up and also somewhat straighten it a bit. (Mind that we’re not only speaking about cost of production, but about marketing, as well.)
Keeping the aging Apple ][, which was still making for the better part of Apple’s revenues, was some of no-brainer, especially, when the company was in need of cash-flow. The Lisa was to go (with as little as ceremony as possibly, compare the land-fill dump), Mac was to stay to revolutionize the computer market and was now to cover what remained of the business market, as well, the Apple III would see some minimal commitment (I guess, for brand credibility), but was otherwise to be forgotten as soon as possible, and the new machine seemed to have been delayed. In the light of this, it may have been also about not risking another machine running too hot, which may have well been the end of the company. Also, there wasn’t really much room for the IIGS in this new, restructured line-up, besides transitioning the Apple ][ community eventually to the Mac. Playing this safe, may not have been an entirely weird idea.
Much of this also adheres to existing 8-bit platforms. E.g., the C64 was already running hot at 1MHz. Transitioning any of this towards the teens range of MHz wouldn’t have left much resemblance to the existing architecture, while other, 68000-based high-speed platforms were already in the making. Which may have also been the major strategic flaw of the 65816: existing systems weren’t to be upgraded into anything with much of a future (if possible at all, considering what was else on those motherboards), while, in the short run, these machines could still pose a major threat to any new platforms which were already maturing in development or were already out on the market.