I can say that the developers are very against the idea of a hard MMR reset at this time. That being said there has been a high majority of feedback especially from that of the higher rank community asking for an MMR reset, as it seems that a lot of players are getting mixed together of various skill levels. When season 18 begins the data accumulated from the role queue beta should not apply directly to everyone’s hidden MMR, but unless they make changes to how the calculation during placement matches work, we are very likely to see the same amount of chaos we have seen in the few days.
Whether an MMR reset happens or not, season 18 will be chaotic in any case.
EDIT/UPDATE:
Participating in the Role Queue Beta will influence the MMR of Season 18 placements.