yes, you can use the same IP across multiple providers; I this mentioned previously (AA will allow you to announce PI address space) as for "I don't see how it

yes, you can use the same IP across multiple providers; I this mentioned previously (AA will allow you to announce PI address space) as for "I don't see how it is technically feasible": read up about BGP and multi-homing: they form the backbone of the internet (just somewhat unusual on a consumer home connection...)