This has nothing to do with the provider, he gives 1000 the same way he gives 100 right now. I know that some routers can't handle even 100 mbps via pppoe (my old linksys e4200, thats why I have now 868L)
I have the fiber in the house, gpon ont ZTE zxa10 f625g. The only thing that the provider does is to change the limit for the pppoe user from 100 to 1000.