> So to paraphrase, the ][ could be upgraded to a ][+?
Yes. Later ]['s used the same motherboard as early ][+'s. Just more RAM, and Integer BASIC instead of Applesoft BASIC.
> Could an upgraded ][ and ][+ be upgraded to a //e? If so, how much further could you take an original Apple ][?
It depends upon what you mean by an upgrade. A motherboard swap was certainly possible, albeit drastic. You could also upgrade the memory, throw in an 80-column card, and do the lowercase mod to have similar functionality to a //e. Albeit, some software would be incompatible.
> The //e could be upgraded to a //e enhanced. Could both be upgraded to a IIe Platinum (without the extended keyboard of course)?
Yes and yes. There were kits to enhance a standard //e. The platinum was a IIe in a different case and with a different keyboard. You could even buy an number pad if you really wanted it. (The motheboard design changed over the years, but that was a production issue not a features or performance issue.)
> The //e, enhanced and platinum could all be upgraded to a IIGS?
It depends upon what you mean by upgrade. A motherboard swap was certainly possible, albeit drastic. Apple even provided a replacement baseplate so that the ports would be exposed.
> Could //e cards be used in an upgraded ][ or ][+ or were they totally incompatible?
The Apple bus was pretty much compatible, with two differences. The slot for the 80 column card/memory card was unique to the IIe. Certain (all?) slot 0 cards would not work in the //e.
> Were IIGS cards compatible with the //e?
To my knowledge, all IIgs Apple bus cards worked in the //e. Well, except accelerator cards (but those had to be tied into the CPU as well as the Apple bus). Certain Apple bus cards had trouble with the IIgs (e.g. CP/M cards). Apple IIgs memory slot cards would not work in the IIe. But I think that the only non-RAM card for that slot was the RAMFast SCSI card.
> You'd think all of this would be in the incredibly detailed wikipedia Apple II pages, or Apple2.org, but if it is, it's not easy to find ...
csa2 is a far more definitive source of information.
Yes. Later ]['s used the same motherboard as early ][+'s. Just more RAM, and Integer BASIC instead of Applesoft BASIC.
> Could an upgraded ][ and ][+ be upgraded to a //e? If so, how much further could you take an original Apple ][?
It depends upon what you mean by an upgrade. A motherboard swap was certainly possible, albeit drastic. You could also upgrade the memory, throw in an 80-column card, and do the lowercase mod to have similar functionality to a //e. Albeit, some software would be incompatible.
> The //e could be upgraded to a //e enhanced. Could both be upgraded to a IIe Platinum (without the extended keyboard of course)?
Yes and yes. There were kits to enhance a standard //e. The platinum was a IIe in a different case and with a different keyboard. You could even buy an number pad if you really wanted it. (The motheboard design changed over the years, but that was a production issue not a features or performance issue.)
> The //e, enhanced and platinum could all be upgraded to a IIGS?
It depends upon what you mean by upgrade. A motherboard swap was certainly possible, albeit drastic. Apple even provided a replacement baseplate so that the ports would be exposed.
> Could //e cards be used in an upgraded ][ or ][+ or were they totally incompatible?
The Apple bus was pretty much compatible, with two differences. The slot for the 80 column card/memory card was unique to the IIe. Certain (all?) slot 0 cards would not work in the //e.
> Were IIGS cards compatible with the //e?
To my knowledge, all IIgs Apple bus cards worked in the //e. Well, except accelerator cards (but those had to be tied into the CPU as well as the Apple bus). Certain Apple bus cards had trouble with the IIgs (e.g. CP/M cards). Apple IIgs memory slot cards would not work in the IIe. But I think that the only non-RAM card for that slot was the RAMFast SCSI card.
> You'd think all of this would be in the incredibly detailed wikipedia Apple II pages, or Apple2.org, but if it is, it's not easy to find ...
csa2 is a far more definitive source of information.