I guess the latency between AWS Frankfurt and GC Belgium should be low enough (5-10ms) to use it for most applications. E.g. storing large amount of data at one provider and renting compute engines for processing at the other one. The latency shouldn't be an issue there, as long as the throughput is high enough.
Can confirm on this, storage for a lot of stuff is in S3 and compute is GCP preemtpibles. Works if you have a small dataset which requires a large volume of compute.