In theory at least, it is valid. I have done something similar in
another tcl <-> python bridge that I did for fun, but didn't achieve
good results in the end. From what I remember, creating a timer handler
instead of using a 20ms sleep complicates the releasing and acquiring
the GIL since you have to create a timer handler to fire now and release
the GIL, then schedule another to fire before any other event fires up
and acquire the GIL, and we would be creating timer handlers all the
time. It would have been better if I left this code in another branch of
that another bridge in order to compare the performance, but I'm really
unsure if this is going to give the improvement that OP is expecting.

Something that I would find interesting to see implemented is a
replacement of the Tcl Notifier, which I would expect to give us the
expected improvement here. Although Tcl is built to allow replacing its
notifier, it is also much more complex to do than doing what the OP is
requesting.

Now, in practice I would call this issue invalid (rejected actually).
There is no code/interest after almost 6 years, closing this now.