I would suggest avoiding one large stretched cluster. There are all sorts of issues that can crop up mostly around resource locality.
- Different networks at each site may require their own pod/service cidr range to not clash.
- You want in cluster services to route to the closest endpoint and not one that could potentially be in another DC.
- Issues can crop up if connectivity is lost to etcd or high latency is introduced.
- An outage at one location could bring down multiple locations (e.g. etcd goes down or a failed upgrade at 1 site)
There are a slew of other issues that can pop up. 