While I'm a strong supporter of your position that the MiSTer (and any FPGA console implementation) is still emulation, it's worthwhile to keep in mind that this will indeed be _a_ future for preservation (unsure about it being the only, and warmer to, but not sold on it being the best way).

Original hardware is great, but it's getting older, and failing. The Super Nintendo / Super Famicom, for instance, uses a ceramic oscillator as a clock source for its sound processing unit, and as the console is designed, the sound clock is essential for keeping the entire system in sync. Members of the Tool Assisted Speedrunning community have been experimenting with parts replacements to resuscitate this clock source with only mixed successes. This is one of many pieces of silicon on these old platforms that will continue to fail as time goes on.

We can't make brand new classic consoles because the parts are just unavailable, and the industry has a well trodden path of reimplementing discrete electronics in FPGA for decades now with great success. If your goal is to keep playing games for a while longer on your OG console, then heck yeah, go for it. It does indeed do the thing. But if we want to be able to preserve this history in as close to the original form factor and play environment as possible, then we have to explore other options, and FPGA system cloning is a grand way to do this.