It might not happen but it’s not impossible since they have done multiples changes in their metrics. The biggest songs of 2019 are struggling to get that certification let alone the new ones from 2020- currently.
Downloads have decreased exponentially, now artists are getting streaming certifications faster, as expected considering the growth of streaming culture in South Korea.
I think the download certifications should go 500k, 1M, 2M, etc. Not even the biggest music market have such a high metric for songs certifications neither the second one.
I know Gaon isn’t like RIAA and RIAJ but my point stands, 2.5M was high even back then let alone in 2021.