The X11 emulation is not thread-safe, thus it is impossible to do a package require Tk from another thread. But multiple Tcl interps in the main thread work. Since "The Flintstones (2014-09-30)" release the X11 emulation is thread safe but many extensions are not, e.g. snack, expect etc. Your mileage may vary.
- Due to Android process start up with respect to the window system the Tcl exec command cannot be used to start other Tk processes.
- The bandwidth of device screen resolutions is broad (100 dpi .. 500 dpi) compared to usual desktop systems. But many elements of Tk widgets are pixel based. This is partly addressed by using icon bitmaps in various sizes but far from being a perfect solution.