Providing 800xA test environments from the cloud
Sure, but not officially tested and approved.
System 800xA carry various certifications (eg TÜV), probably few including cloud based computing.
Last I heard from a project making some cloud testing was that the networking solution offered inside the cloud was restricting multicast traffic between the servers. RNRP is a firm requirement. RNRP require free multicasting.
Traffic with the physical world outside the cloud could be realized with RNRP Tunnel Areas, a tunnel area does not need multicasting, but is hardly a viable option for server to server traffic inside the cloud.
The 800xA HMI is dependent on low latency between servers and clients; thin clients running sessions in cloud based RDP servers is probably recommended over thick clients; yet, the most premium experience comes with high CPU frequency clients (the more GHz the merrier).
Having control network wired into the cloud is another discussion; traditionally the control networks have been a sacred place with few invited nodes. I guess you could route MMS from Earth to Heaven, but it need testing and formal approval by authorities.