On the IIe you can change the terminal or modem (DTE - DTR?) on the super serial card by changing the plug position. Is there a way to do that on the IIgs? Make slot 1 the modem and slot 2 the printer?
No, there's not a way to change DTE vs. DCE role the way you can with an SSC card. You can change the nature of the port and the commands it accepts via the control panel (specifically printer vs. modem) but it doesn't change the electrical role of the port.
I must confess that I have not found much time yet to really get into tinkering with my own IIgs setup, but didn't one of the ways they attempted (for cost-cutting and corporate-image consistency purposes) to "converge" the Apple II vs. Macintosh departments within Apple involve unifying the peripheral lineups to some degree? I was under the impression that a IIgs had the same kind of serial ports as a contemporaneous Macintosh (namely RS-422/423, which can interoperate transparently with legacy RS-232 gear _regardless of whether as DTE or DCE_, by connecting only a specific subset of the pins in the cable in either case). While it has been years since I physically looked to see if that is in fact the case, the hypothesis is partly corroborated by the fact that a IIgs can do LocalTalk (not actually impossible with a traditional RS-232 port, at least if the right serial chip is controlling it, but not nearly as easy).
We're all in violent agreement - the SCC-driven ports on the back of the GS are the same as the Mac ones, and it was in part to consolidate product offerings (and look). The chip itself (Zilog SCC or the SSC's 6551) can be wired to play either role, it's true. And the Super Serial card makes that easier to do with a single cable by breaking out the role on the card and "rewiring" your cable for you. But there is no such thing on the GS or the Mac, so you need to build/buy either a "printer" or a "modem" cable that does the rewiring for you. Thus the computer plays whatever role you want... you just need to use the appropriate cable.