I think a system where the initial rent is set at market value followed by low annual increases (inflation or 2%) would be a pretty decent one. The landlord gets market value initially, the tenant has certainty as to increases for a period thereafter. Likewise, a system where the tenant as absolute security of tenure for a period is, I think, a good idea as well.In France, 3 years is somewhat the norm. However, during this period, LL can give notice in a limited number of situations (a bit like currently in Ireland). Note: the tenants might also have to give 3 months notice if they break the lease without justification.
Once in place, the LL can only review the rent within an indexation system (if the lease allows it) and between lease (within some limits).
I think that the 6 year cycle currently suggested is too long. It won't be attractive to landlords. 3 years, as in France, would be better. It does give the tenant security as to tenure and rent without tying the landlord's hands for too long.