Python is, despite its simple appearance, a much more complex language than JavaScript. A V8 equivalent for Python is certainly possible, but would require even more work than went into creating V8 itself - who would be motivated to spend that much effort on Python?
Dropbox? They seem to be the company driving Python nowadays, but gave up trying to speed up Python in favour of writing "performance-sensitive code in other languages" [1].
PyPy uses a meta-tracing approach in an attempt to reduce the amount of work required. Its speed is impressive, but I'm sure meta-tracing leaves some performance on the table.
Another way to reduce the amount of work required would be to support only a subset of the language - for example, a V8 equivalent for MicroPython rather than for full Python. I'm sure this could be made very fast, but it would have very poor compatibility with existing Python code, so what would be the point?