Not very plausible, no, as Satoshi probably used hid his IP very well, etc... so they would have nothing to go on.
In any case, even if they did, so what?
i see absolutely no reason why the cia would bother. they have much more pressing things to do.
i would be intrigued to know how possible it would have been for them to track him down if they'd put their minds to it. i think the resources of an entire nation state might have one up on one anonymous guy or group.