Scaling cluster connections independent of cluster size/tier
Currently whenever you want to increase Atlas cluster connections, you have to scale up Cluster Tiers. When an application doesn't require additional disk storage but only additional connections the additional cost is difficult to justify.
"Unfortunately larger and larger numbers of connections require more compute" We understand that and there's a difference in compute ability between M10 and M20 already, that's why we have them as different tiers. So ideally, the number of connections available in M20 should be higher as well.
Also, can you clarify if the number of connections is an altas-level limitation or a cloud provider-side limitation? If it's a cloud provider-side limitation, which instance type are we using in AWS? Because I've not experienced the same in mongo on-prem deployments.
The first-order cost contributor to an Atlas cluster is its compute (memory and CPU) requirements rather than storage size. Unfortunately larger and larger numbers of connections require more compute. Note that you may be able to optimize with connection pools.