Yes, there are replacements. But if you use a teensy 4.x you actually don't even need one of these. We are using a Teensy 4.1 to emulate old arcade vector games including the sound chips. A teensy has more than enough raw calculation power to emulate multiple of these audio chips at once and generate a I2S signal for an external audio DAC.
I can only speak for myself—though I think @jonathan322 was largely pointing out that efforts are being made to preserve these circuits from total extinction—but there are damn good reasons I’m using the real deal rather than YM2149 “emulators” for my project, the largest of which is the desire to teach an old dog new tricks, something that can’t be done with a simulator, with authenticity, nostalgia, and the challenge of doing so coming in tied at a very close second. In fact, a specific product that uses a simulator rather than real hardware played a small part in pushing my desire to create this synthesizer over the edge.
A large part of the issue is precisely that so-called emulators of old 8 and 16 bit era audio chips that we still haven’t managed to fully reverse engineer are just that:
So-called emulators. I used quotation marks above because they are not emulators at all. Emulation is the attempt to perfectly recreate hardware—and if applicable, software (such as a boot ROM) required for it to operate—in a virtual environment.
Simulation, on the other hand, is the recreation of how one
interacts with a piece of hardware, and outputting something very similar to the results of doing so.
As an example, in the case of the YM2149, which is basically just a square wave generator with a bunch of shift registers and few PLL clocks along with a pseudo-random noise generator and a few DACS, not a single YM2149 “emulator” works this way. These simulators simply accept the values one would send to the chip, then return the audio the chip would return, in the best case scenario, based on measurements of the chips voltage output or PCM output. None of the code actually replicates the manner in which the circuitry works. Interestingly, the YM2149 is basically a state machine, and a large portion of its circuitry could be recreated using FlexIO, much like accurately implementing circuits using an FPGA.
Even the best emulators of legacy computers, gaming consoles, and arcade machines don’t actually emulate their respective audio chips.
To return to the overarching thesis: One cannot use a simulator to develop new means of programming/controlling a piece of hardware with any guarantee such techniques would actually work on the real thing, which is precisely the goal of projects such as the one I’ve referred to in this thread.