Tankiness of buffed phantom dancer could be quite strong.

So Riot is considering buffing the damage reduction of phantom dancer to 16 percent. That is the equivalent of a 20% increase in maximum health (except that it won't increase the %max health damage coming from enemies). If you have 4k health, that's 800 health worth (and again it doesn't increase enemy %max health damage). So phantom dancer would provide more tankiness than a warmogs in addition to providing great utility and some offensive stats. Even if you don't need the crit or attack speed, a tank, juggernaut, or bruiser could consider picking this up as a final item simply because of the tankiness and utility.

For comparison, cinderhulk provide 400 health plus 15% of bonus health. If you had 2k base health and 2k bonus health (late game 4 items can get you there), then cinderhulk provides 750 health and phantom dancer provides the equivalent of 800 health which does not count as health versus %max health damage. The 12% movespeed near enemies, 5% roaming movespeed, and ghosting are all useful. The attack speed and crit would be useful for some champions.

Champions who could build tank and potentially synergize strongly with the item: volibear, darius, tahm, warwick, vi, nocturne, mundo, hecarim, olaf, trundle, skarner.

Champions building tank who might situationally use it: alistar, chogath, gnar, malphite, ramus, udyr, nasus.

Right now you are thinking "what, build a phantom dancer on chogath? that's stupid." That's kind of the point. Even with the stat bindings, the damage reduction on phantom dancer could be so strong that even a tank chogath might decide to pick it up.

So for example if you built chogath full tank with cinderhulk, tabi, banshees, randuins, and had 900 health from feast stacks rank 3 ultimate, at level 18 you would have around 5100 health (I know this isn't an optimal build for cho, but go with me). The phantom dancer would add 1050 health that doesn't count towards % of max health damage -- in addition to all of the other stats it adds.