No, ACS 5 won't have a Tcl version. I suspect, though, that there will be folks who will be satisfied with ACS 4 and will continue work on it. Just as people are still fixing OpenACS 3.2 today. ACS 5 won't be "real" for many months, so presumably there will be real sites developed with OpenACS 4/Tcl. Once real sites are up, needing to be extended and maintained, there will naturally be a desire to continue improving the toolkit.