scorecard:

• safety: the standard Tcl interpreter is runtime-safe, and Safe-Tcl is all about system safety.
• GUI: Motif GUI provided by Tk, with Windows and Mac in development. I don't believe they're going with a portable GUI interface: a module negociates the user interface API at runtime.
• concurrency: no.
• FFI: very clean and simple, but only for "trusted" code.
• Module system: Tcl is traditionally weak on this, but I hear they're actively working loading untrusted modules. I'm not sure what the strategy is for namespace management.
• Exceptions: catch/throw, as opposed to try/except.
• Types: Tcl has not objects with inheritance, though there are a number of "aftermarket" options for this. However, the standard library interfaces don't use inheritance. I hear work on this is in development.
  The tcl-dp extension provides an interface to sockets, but I don't know if they've come up with or enforced any security policies; i.e. I don't know if the untrusted code can get at the tcl-dp API.

Licensing

Tcl is distributed under an MIT/X/Berkeley style copyright. As long as that continues, I see no IPR issues.