Replace? I doubt it. Or rather, I think they wouldn’t gain much from doing it, as most packages are actually just imported directly from Arch Linux anyway; therefore, they would not save much time in package maintenance.
Right now, Snap and Flatpak supports are installed by default, but they are merely additional and optional sources of software. Also, Pamac can manage Snap and Flatpak (you need to enable an option to see Snap or Flatpak support in Pamac, which is not enabled by default).
It is still pretty controversial in the Linux community, especially Snap from Canonical (people seems to tolerate Flatpak a little bit more). As for myself, I don’t care about their presence in Manjaro that much, although I did not have that much of a great experience with Snap; I experienced less issues with applications shipped with Flatpak (it might be not related to Snap in itself, but rather how the build is done). However, I prefer using the traditional package (official repos or using build files from AUR) than using Flatpak, but I have to admit that I use three applications that I installed from Flathub (Discord, Microsoft Teams and Flatseal).