Re: Flogging a dead horse
tl;dr version of the extended(!) comment below... The C65 would have (sadly) flopped because no-one would have been willing to pay a premium for a new 8-bit machine in 16/32-bit centric 1992, the C16 and Plus/4 flopped because they were turned into something they were never intended to be, Amiga 600 was the Amiga's jump-the-shark moment, Amstrad GX4000 *proved* that no-one wanted new 8-bit formats by the 90s and the Atari XEGS was really just a trick to get XE computers into computer-resistant shops rather than a genuine (and crap) attempt to compete with Nintendo.
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The C65: Sorry, but nope. The C65 wouldn't have made an ounce of commercial sense by its likely release date, circa 1991-92. C= made the correct decision there (for once).
As nice as an improvement on the C64 as it looked, it would still have been an 8-bit machine coming out at a time when the market had already shifted to 16-bit (and even the Amiga was peaking).
Yes, C= sold the C64 itself until they went under in 1994, so the market must still have been there and *that* made sense. But it's safe to assume that was *because* it was cheap both to manufacture and sell and had a large selection of *pre-existing* software. The C65- with its integrated floppy- would still have had to have cost more in both respects, and it wouldn't have been able to command the premium they'd have had to charge. Anyone who had the extra money would likely have bought an Amiga, Mega Drive, or whatever instead.
Diehard C64 fans may have bought it, but- just like any format fans- they tend to confuse their enthusiasm with market importance. It would have been a niche fan success, but a mass-market failure.
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The C16 and Plus/4: These were pointless (and unsuccessful) because the original design was never meant to replace the C64. From what I've read, Jack Tramiel was paranoid about the Japanese bringing out an ultra-low-cost computer and undercutting the competition (as they'd done in other markets), so he wanted to pre-empt them. The cheap rubber-keyed Commodore 116 (which I don't think was ever seen in the UK) was apparently closest to the original intention.
After Tramiel left C=, and the threat didn't materialise, management didn't know what to do with the design and repurposed it into (e.g.) the Plus/4 which pointlessly competed at the same price as their own C64 despite inferior graphics and sound and incompatibility with the huge C64 software base.
The irony is that Tramiel's aggressive price-warring had driven the cost of the C64 down so far that it *was* already a cheap option, at least in the US, so there probably wasn't the impetus for something only slightly cheaper, but inferior. Even if C= would have made more money on that cheaper-to-manufacture design.
(The case has also been made that while the C64 won the US price war for that reason, it was a pyrrhic victory, as they'd done so by squeezing the profit on it to a minimum. It certainly didn't do much for the company's long-term prosperity or survival).
Other irony is that while the theat didn't appear directly in the expected computer-based form, the Japanese ultimately *did* hit the C64's market share in the US with the success of the NES over there, since many- or most- C64s were bought as glorified games machines anyway.
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Amiga 600 and 1200: In hindsight, the 600 was when the Amiga was definitively knocked off its pedestal as the "hot machine". It was meant as a cheaper model (the Amiga 300), but they couldn't get the cost down enough and mis-marketed it instead as the replacement for the A500, which it didn't improve upon overall and in some respects was inferior to.
The 1200 was a bigger improvement and- in hindsight- the "true" replacement for the 500, but it was more of a "keeping up" exercise after the competition finally caught up with- and started overtaking- the Amiga 500. It soon fell behind again, then C= went bankrupt.
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Atari XEGS console: Interesting one.. this always *seemed* like a cheap attempt to compete against Nintendo on the cheap without putting the marketing or software support behind it (i.e. typically cheap Tramiel-era Atari). But years later, I came across a statement from Atari marketing at the time of its release, which suggested that it was really more of a ruse to get the XE computer line to stores and consumers that otherwise wouldn't be interested. (IIRC the XEGS was almost always sold with the keyboard anyway, making it pretty much a 65XE computer in disguise).
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Amstrad GX4000: Based on the same hardware as the significantly-improved "Plus" versions of the CPC computers, this looked pretty impressive by 8-bit standards (better than the NES, at least as good as the Sega Master System?) and would have been a hit if it had come out two or three years earlier. But it was a "new" 8-bit machine being judged against the likes of the Mega Drive, and that's why it quickly became a joke. (Which- IMHO- reinforces my point about why an 8-bit C65 coming out circa 1991-2 would have flopped for similar reasons).