Melbourne for North will be the change in top 8.
I agree with that as a possibility. However, there is usually at least 2-3 changes to the top 8 though, so I'll just categorise them according to my opinion at the moment:
Likelihood on teams making the 8 from outside the 8:
Likely: Melbourne and St Kilda
Middle but leaning towards likely: Port Adelaide, Collingwood and Fremantle
Middle but leaning towards unlikely: Richmond, Gold Coast and Essendon
Unlikely: Carlton and Brisbane
Likelihood on teams missing the 8 from inside the 8:
Likely: North Melbourne
Middle but leaning towards likely: Hawthorn, Geelong and Adelaide
Middle but leaning towards unlikely: West Coast and Western Bulldogs
Unlikely: Sydney and GWS
May be strange that I put Adelaide and Geelong as leaning towards likely. Adelaide I feel haven't improved their list in the trade period but only lost depth. As a Richmond supporter, I can tell you what can happen if you don't improve your list when improvement is needed (2015-2016).
Hawthorn, North Melbourne and Geelong lost a bit of experience, and Fremantle 2015-2016 is the example for those three teams.
I think the likelihood of all four missing the top 8 is slim, but individually this is how I rate their likelihood. Having said that, I don't think it is unreasonable to think that 2-3 of them will miss the finals next year.