The default Marketplace/CF config is great for getting started, more greenfield usage, etc. But it doesn't accomodate more complex (but common) situations. For instance, we've just completed a complete overhaul of our AWS infrastructure. The project had kind of shuffled into AWS. Started with one account, with lifecycle environments only segregated via security groups. After accepting that that was a VeryBadThing, went to VPC's per environment, with AWS account segregation (one for production and pre-production, another for all dev lifecycle environments), we've now moved to something a bit more sophisticated with accounts/vpcs per lifecycle environments, dedicated shared accounts/VPCs for ingress, data vault/logging, management, etc with IPSec tunnels between them all, as opposed to VPC peering.
Sorry about the excruciating detail, but just wanted to provide context. So, in this scenario, shoehorning in Datomic Cloud becomes a bit difficult. Especially in conjunction with the current app/system assumptions (bring on those multiple query groups please! :)). For instance, my plan was to give each of my devs their own sandbox Solo instance, this won't scale well (there are 40 of them ;)) of they each need their own VPC, never mind the other issues. And I guess that might be basically a separate but related request, where one could stand up multiple 'systems' in a single VPC