Imo, multi-sig setups will likely be the standard for enterprises, institutions, large merchants, etc which are using either L1/L2, because they have a need for increased security and also to segregate duties so there's not too much power in the hands of one individual.

Whether or not multi-sig becomes widespread among individuals I think really depends on the UX that can be built around it. Right now, multi-sig for L1 is daunting for many users, especially the less tech-savvy. If the difficulty can be abstracted away easily, without sacrificing too much in security or becoming too expensive, I could see it catching on more widely.