Doesn't Backblaze just have a single datacenter? If so, I think they're pretty limited in who they can partner up with like this. That is, they could only partner with companies who are in the same datacenter as them (or very close, network wise, due to latency) that they can connect directly to.
Backblaze has two facilities, one in California and one in Arizona. They're limited to anyone who can reach their network edge through a network port in their datacenters, but theoretically, you could ride fiber to their network ports from other facilities.
I would expect that as this grows (and it will, cheap, reliable storage and all), their network footprint would extend into more facilities (scale is required for this to be cost effective though).
Latency is not an issue until you're pushing GB/sec and crossing an ocean, and even that is feasible (lots of resources at https://es.net/ for that use case).
