I'm about 20kloc in to a (not public) nMigen project, including a UDP/IP stack, various peripheral drivers, a DSP pipeline, and some custom networking code. So far I think "do the advantages of being able to metaprogram outweigh..."is a resounding "yes", but I came to it with extensive Python experience so it feels like a very natural fit to me, and given how other attempts at embedded metaprogramming go (Tcl...) I'm not sure Python is easily beat. Being able to integrate with numpy for DSP work, pytest for simulation and testing, Python packaging (such as it is) for distributing modules and managing dependencies and versioning, and simulating inside Python too are all additional compelling advantages.

nMigen is a pretty fledgling project so there aren't a ton of big projects in it yet, but for example Luna[0] (from the makers of the HackRF) implements a full USB stack including USB3 support, with enough abstraction that you can create a USB-serial converter inside your FPGA using two I/Os for full-speed USB and wire it into the rest of your project in about ten lines of Python[1].

[0]: https://github.com/greatscottgadgets/luna [1]: https://github.com/greatscottgadgets/luna/blob/master/exampl...

Migen, the Python-based project nMigen is based off, has been around for longer and has some large projects, such as LiteX[2] which uses Migen to glue together entire SoCs, including peripheral cores such as GigE, DDR3/4, SATA, PCIe, etc, all written in Migen, and is pretty widely used. It also pulls in Verilog/VHDL designs (such as many of its CPU core choices) since it's easy to pull in those from the Python side.

[2]: https://github.com/enjoy-digital/litex/