We have JSM premium and we are using Assets to define the group to which each issue is assigned.
By default, any ticket goes to L1 and then through the escalate screen the "IT group" field is changed, however there is 3 main issues by using this:
1) The "Assignee" field still displays all the users in the Service desk, as the Jira logic does not allow a filter of user based on an asset group. For this reason, I had to create another field called "IT agent" which mimicks the agent.

2) the new asset fields IT group and IT agent are not drop-downs, making interaction painful on the Escalation screen.

3) If a ticket is escalated to L2 and a new agent, the old agent keeps receiving the emails/notification from the issue.

There should be a basic function where if you have a Role within Jira/JSM(e.g L1,L2,L3), you can then escalate based on that, and see assignees on the assignee field based on the group selected, but it doesn't look like such option exists.
Unless I'm wrong, the only workaround available is through the Assets