Client want to move the Dynatrace Managed to new set of servers.
a) don't want reinstallation of OneAgent
b) don't care about historical data
Thus, I proposed them to add the new set of servers to join the cluster of existing Managed, then deployed a new ActiveGate, then remove the old existing Managed follow by removal of old ActiveGate.
Would it works?
If it were a new AG on the existing managed instance then you would be fine and the agent would see the new AG and add it to the connection list. The issue is that you are adding a new managed instance which means you will have to install agents from that instance as a best practice. Agents are built to connect to the instance that they are downloaded from.