47 kOhms was no doubt chosen as a compromise. From a noise perspective, you'd want it to be higher, but from a peaking / damping perspective it's hardly sufficient for some cartridges even with best-case capacitive loads as-is. You can accommodate more capacitive loading with lower resistance, but the top end of frequency response invariably is lower as well.
The best thing to do would be integrating a small FET buffer into the cartridge itself, thus making it active. I imagine doing so without negatively impacting move mass (for parts and potential extra cabling) or wrecking compatibility would be a challenge, but not infeasible. Integrating either the whole preamp or a buffer into the turntable would already constitute progress as well. (It has been done in the past but the circuits of the mid-1970s weren't exactly premium quality.)
Plan B would be a radical change in design approach, going from voltage input to current input and treating the cartridge as a current source instead (which would allowing using a transimpedance amplifier and applying some tricks from instrumentation). I have no idea whether the increased damping would negatively impact anything, and you would no doubt have to individually accommodate each cartridge type to get the right frequency response out of it. At least the response would already be a 1st order dropoff natively, so fairly little in terms of EQ should be required to get an RIAA out of it.
