It makes absolutely no legal difference, it makes no functional difference. You already noted anyone can do it by mining a block, which you can do at a fairly minor cost using nicehash or other similar services, but you don't even have to because as was demonstrated at the start of the discussion major miners (and likely a majority of hashpower even!) were already ignoring that op_return limit in their policy! (and doing so THANKS to motherfucking luke and his outspoken stupidity causing miners to erroneously believe that the existing filtering policy was politically loaded and try to diminish their income!) So it's already there, even before all this discussion. The world hasn't ended.
Given that the vast majority of blocks are produced by institutionalized mining, any mining company that attempted to do such a thing, perhaps through a bribe or similar, would quickly get caught and go viral on the internet, and most likely face additional consequences including potential criminal charges, depending on the country they're incorporated in.