Prediction for Tank Reworks
The Big 5:

Amumu
The Curse/Magic Amp Tank
- New Passive
- More emphasis on amplifying magic damage
- Relies less on landing Q/doesn't need to land a Q or flash to be useful late game
- Most deadly Tank for teams to be near damage-wise
Sejuani
The Anti-Mobility Tank
- New Passive
- Makes use of the new Grounded debuff throughout kit
- More focus on longer duration/constant slows than one big stun initiation through R
- Retains overall damage, but more spread out and sustained
Maokai
The Tree Tank (Vision and Roots)
- More "Rooted" effects throughout kit
- E is more powerful overall, more focused on utility than damage
- Potential expanded/replaced use for ultimate (Riot hates basic aura effects)
Malphite
The Anti-Attack Speed Tank
- Potential passive heavy changes
- More focus on slowing attack speed
- Reduced burst damage in favor of more utility
- Power taken from ultimate and spread out throughout kit
Nautilus
The Lock Down Tank (Single Target CC)
- Reworked W into CC/Utility focused spell (removed DoT attacks)
- Slight Q changes to better differentiate from Thresh and Blitz
- Potential new E/changed E
Others:

Poppy
- Damage shifted around (relies more on landing E for damage, Q damage perhaps shifted more towards flat than % damage)
- Changes to W passive
Rammus
- Changes to help before coming VGU
- New Passive
- Potential ultimate changes
Shen
- Changes to Q
- Potential changes to Flash/E interaction
Skarner
- Changes to help before coming VGU
- Potential passive, Q, and E light changes
Volibear
- Changes to help before coming VGU
- Potential changes to passive, E, and ultimate
Zac
- Changes to Q
- More focused around long range initiation/CC, shifted slightly away from damage
? More explanation required how adding the Groudned debuff somewhere in her kit would make her pick/ban