@Riot Please take care before turning Rylai's into tanky item
a) It would be heavily abusible by hypermobile AP champions in tank builds (tank Fizz, tank Ekko, tank Akali). Arguably, permaslowing hypermobile tank is much worse for game health than permaslowing immobile mage.
b) If it's AP gets nerfed, we desperately need another high-end AP item.
I don't say "don't do this", I just say "watch out for consequences".