In practice, there is a strong temptation for a provider to build exit barriers – to not provide reversibility tools – in order to have commercial leverage to avoid losing a contract.
It is quite common to see exit benefits from a system – decommissioning costs – exorbitantly high compared to what they should be. The most common cause being precisely the lack of reversibility tools. Ideally, the cost of reversibility to be paid to the supplier of the outgoing system should be zero.
Any archiving system is equipped with very flexible means of injecting documents according to the formalism transmitted by the client. Based on this observation, the export formalism can be free insofar as the import formalisms are adaptable.
The only constraint is really the completeness of the export, bearing in mind that if traceability, for example, is not exported, the evidential value will be affected. The completeness of the export and its intelligibility are therefore major criteria, rather than its formalism.