Using an actual HDL implementation to begin with has been shown to be a very effective approach, and that's basically what MiSTer FPGA has done with great succe

Using an actual HDL implementation to begin with has been shown to be a very effective approach, and that's basically what MiSTer FPGA has done with great success. However, MAME probably supports more emulated platforms/systems (and some MiSTer platforms may not be supported by MAME.) That being said, what I think you might be suggesting is that the declarative structural and signaling specification (and possibly data types, etc.) could be shared between software emulators like MAME and FPGA emulators like MiSTer FPGA. I like the way Migen (for example) acts as an integration platform for multiple hardware models and makes it easier to specify a system from existing components.