I see the term "SNR_2500" is often use to make it clear. Is it useful to use this SNR definition in some contexts?  Is this kind of convention used in other digital modes or communication systems?

Edit to add: I should have made it clear that my expectation is that the noise power used for SNR would be that in the range of frequencies occupied by the FT8 signal (or perhaps the range of frequencies seen by the FT8 detector).