One way is to provide Python(python stdlib might be enough for simplicity) gradually, e.g. providing a Python binding for Tcl so for the future, you can write all new piece in Python, and it is either used directly or converted to Tcl behind-the-scene.
If a startup wants to displace an entrenched tool from Synopsys or Cadence, the underlying algorithms (millions of lines of C++ code) must be better. (And once that happens, they'll be acquired by one of these 2.)
On the front-end side though, areas like verification, debug, and various lint checks, I think there is more opportunity for smaller players to introduce point tools with better customizability & scripting interfaces.
Ultimately I think the industry is stuck in a local maximum, where the frictional costs of rethinking overall methodology, e.g. from SystemVerilog to Chisel, is too high to justify the change, even if the end result would be marginally (or greatly) better. (Not an endorsement of Chisel, just an example.)