Hi Naishadh Sevalia,
principially, all Java EE applications should be migratable (IMHO). What's the question is the effort necessary.
One of Windup's tasks is to help estimate that effort.
Of course, apps can be considered "not worth migrating" if the effort would be too large.
But more often case is that the migration effort is unknown, and therefore the risk is higher.
We hope that Windup will help to eliminate that situation.
Hope that helps.