Not really useful, if I'm honest.
Costs are far, far higher than traditional metro systems. Even non-traditional 4th Rail rubber tyred metros like in Paris, Montréal or Sapporo get the benefits that a linear motor would, at least in terms of steeper inlines and tighter turns as well as faster accelleration and decelleration.
I think there could be an application of a linear motor in a metro like system, but I feel as if the costs would not only be extortionate for inital construction, but the complexity would be too much for any non-Japanese city.
Therein lies an interesting point. Only Japan has invested in suspension monorails, standard monorails and high speed maglev, despite the fact that standard conventional rail is cheaper and easier. China could do it too, but that depends on the Chinese being interested.
Honestly, I think light rail metro the DLR in London or the LRT-1 in Manilla would be easier to implement, even if you need the need to deal with steep inclines or turns, rubber tyred metros would be much cheaper to implement.