Tcl bytecode is the instruction set targeted by TAL
... the current Tcl bytecodes are defined at a level that is meaningful to Tcl, not at a level that virtually any other bytecode operates at; very few bytecodes have an opcode for "increment-hash-entry-and-fire-attached-traces"! Given that, you're either just producing another language reimplementation (like Jacl) or you're taking on the hard task of defining how to go from Tcl to the fairly-common low-level register-based bytecode engines that so many other languages use. Which would be nice and useful, but is a really huge (and definitely complex and deep) task...
Byte-Coded commands are sometimes faster than commands implemented in an external language like C. MS, Tcl Chatroom, 2013-12-31, offered these reasons: