There is one case where I find relevant the intention to access legacy IN services: when IMS is used to extend an existing circuit-switched telephony service towards VoIP. Basically, the user keeps its circuit-switched telephony services, but sometimes happens to use VoIMS instead of VoCS. In this case the same services must be shared between the two networks, and one option if for IMS to access the legacy services.
And by the way, why would telecom experts now resolve for IMS the service interaction management issue that eluded them for so many years in the circuit-switched network?
Unfortunately it does not work this way. In order to support multimedia communication you need to have the right architecture in the application layer, and legacy monolithic servers need to be re-engineered for this. There is no magic box to change the situation.
This is how I see it, but in order to comply a minimum with the entity introduced in IMS specifications, this orchestration must have something to do with the SIP protocol. Service orchestration related to web services, implemented via BPEL or something else, should not be mixed up with what can be done at the SIP level.