1) External drive must supply termination power (the power supply in the Plus is too feeble to do the job, so the design team decided that the external box should supply term power).

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Is that necessarily so? The floppy port on a Plus has the power to drive an external disk. so why can't the psu provide exterminal termination power. I took my figures from this site: http://www.scsita.org/aboutscsi/SCSI_Termination_Tutorial.html

Effective termination resistance = 132 ohms

Nominal voltage = 5 volts

Nominal term power = 0.19 watts

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That math isn't quite complete, and also contains some implicit assumptions. Here's my calculation for the Plus: The termination network for each line presents a 500-ohm resistance to ground from the 5-V supply (in round numbers). That's 50mW per resistor, when no I/O driver is sinking any current. There are more than a dozen lines, so there's the better part of a watt just heating up the terminators with no SCSI device attached. Once there is an attached device, the peak load increases to a couple of watts. Normally, that wouldn't be a big deal, but given that the Compacts were on hairy edge of overheating without SCSI, the additional load was ultimately deemed too much (remember: the floppy drive's power has to be considered when computing the peak load on the supply). A hint of an internal debate can be seen in early documentation showing the Plus supplying termination power. Production models omitted this feature.