Any big publisher not named 2K, Activision-Blizzard, Bethesda, Deep Silver, EA, THQ Nordic, Ubisoft. Even then, only Nordic makes GOG releases a priority.

My money would be on big Japanese publishers being the least likely to go for it. Squeenix, SEGA, Capcom et al. Japan seems so sclerotic when it comes to gaming and culturally in general, no wonder their presence in the western gaming market has stagnated for years now.

Second least likely would be store owners like Ubisoft, at least for anything released in the past few years. Why put up with Uplay when you don't have to, right?