Someone attempting something like this. But IMO the end result still has the fast chip running at wrong frequency messing up games. viewtopic.php?f=25&t=80651
Anything that ran on DOS, Win 3.x and 9.x won't utilize 4GB of RAM and generally won't support multiple cores. And while you have a sweet new motherboard that can run PCI and ISA cards, the number of these cards continues to decline.
Consoles have gotten mods that improve them such as grabbing the digital video and bypass the analog circuitry and then scaling that and outputting HDMI. But computers are also getting mods, look at the XT IDE, the Amiga Vampire mods, etc.
The "new" retro consoles fall into one of three camps. The official ones are normally emulated on lower-powered ARM hardware with a fancy case. Some 3rd party ones are on custom SOCs that almost all universally suck (Jeri Ellsworth's C64 is an exception to this). And finally, FPGA-based systems which attempt to simulate the system at a hardware level.
Of these FPGA is seen as the most accurate, though they are still created by humans and may not be 100%. Then again original hardware had different revisions and sometimes there were incompatibilities, the Sega Genesis/Mega Drive switch Yamaha sound chips, and some early games don't sound right on new systems, and vice versa with some later games written for the newer chip. The SNES changed graphics chips consolidating them and some games have visual errors on the later hardware. Then going down to two consoles of the same revision sitting on a shelf, components in them are made within a range with some being accurate to within 1-5%. So you and a friend could each buy one but one of you has a clock chip that runs ever so slightly faster, so what is accurate to an original console.
The FPGA cores can improve on the original consoles, the Genesis/Mega Drive core in a menu lets you switch the Yamaha sound chip. Old console limits to how many sprites could be displayed on a line and then would flicker if there were too many. You can keep this behavior or enable an option to increase the limit. You can overclock just a part of the system like the SNES's addon SuperFX chip where some games ran at 15fps or fewer, the overlock improves performance. Some cores add save states which helped with old games that didn't have a way to save.
Old computers have also gotten this treatment from the Amiga, Apple 2, Atari ST, C64, MSX, etc. And yes even the IBM PC. There is an FPGA core named ao486 which can simulate a 486SX at around 33-40ishMhz. It has an ET4000 video card, a SB Pro that has real stereo OPL 2/3, CMS, and an MPU-401 that can interface to a Raspberry Pi to get MT32 support, as well as accessing Fluidsynth. It can run DOS, Win3.X, and Win 95/98.
There's always the possibility of small runs of new cards like the Orpheus, the Ultimate SB64, and even a custom real Voodoo 5 6000. But original chips are a finite resource that will be eventually exhausted. The time is now to start figuring out how everything works and creating accurate simulations. The FPGAs are a programmatic design of just how a system worked, they are portable between multiple vendors, and if you have the resources you can take the design and creating your own IO systems create an SOC that does the same thing.