I have a Visualforce page exposed as a Tab with heavy javascript and it uses AJAX toolkit. We are in the process migrating to Lighting Experience and this page seems working fine at high level in Lightning and it even uses GETSESSIONID for the AJAX calls.
Have you noticed any issues with similar pages in Lightning? Is this a good candidate to develop completely using Lighting Components but I don't see a reason if it is working fine.
Please let me know your insights.