Anyway, my take-away is that a simple runtime check for Tcl/Tk 8.x+ could be a viable solution.
This pretty much exactly describes what is happening in the current master branch.
I'm slightly baffled that the default is to*not* use tabs, because iirc it should use them. But then, the choice whether you get tabs or not can be overridden via GUI preferences, so maybe I just forgot to reset then at some point...
Note that Windows and Linux currently also use non-tabbed preferences by default. From your mail I gather that this is just an oversight?
Christof