You can do multiple consoles over a serial connection with something like tmux or screen. But you can also do networking... you can configure PPP using pppd on the pi to run over serial to either CE or Linux on a jornada, the same as the old "direct cable connection" in windows. Then you can run telnetd
(or better ParanoidTelnetD
https://github.com/ColumPaget/ParanoidTelnetD) on the pi and use telnet for console work
(I am assuming there is a telnet client for CE available somewhere
).
The big problem is of course speed... serial
(on the jornada at least
) is far slower than a 10/100 card, max 230400 bps
(maybe limited to less in CE
). Although worth noting that the serial port connected to the IrDA transceiver can do 4mbps. I'd be interested to know what actual speeds can be achieved from a 10/100 card.
In terms of power consumption, even with a serial transceiver
(which typically will output +/-8V rather than the standard +/-12V, because that's enough for pretty much any 232 device
) the power consumption is going to be way lower than a PCMCIA card. I could find actual figures, but I'd imagine serial idles at almost nothing and uses max maybe 30mA for TX, whereas PCMCIA ethernet is going to be perhaps 100 mA or more at idle and several hundred mA for TX.