Looking forward, it seems possible for Amaranth to be a full fledged language unto itself without needing python. One could maybe use python as an embedded macro language still -- which could be very powerful.

One of the reasons amaranth (and other neo-HDLs) is so great is the full-fleged seamless integration with the host language. Generating DSP filters using the numpy for all parameters, creating CRC structures, diffent logic for different word widths, ... .

This is all feasible with SV or an embedded Macro language as well, but you'll either have to live with a poorly documented meta language (as not a whole lot of people are using it) or heavy missmatches between the meta language and the "real" language. Cocotb very much suffers from this for simulation usage.

And, tbh, if it can be nicely implemented in the host language (which IMHO is the case with amaranth, less so with migen), I don't think there are many benefits by being standalone.