It has been around since svr3, at least.
As far as having multiple SCSI channels per controller, you can do
that by having more than 7 or 8 targets per controller:
c0t0d0s0
...
c0t7d0s0
c0t8d0s0
...
c0tfd0s0
or maybe split the channel number out as a separate digit after "t"...
Making the Target ID incorrect by incorprating the channel number is a bad
idea. This would only confuse people. The channel/bus number logically comes
after the controller number and before the target ID, so that's where it should
be in the naming scheme.
Leonard