PI 7.5 interface architecture possibilities

Dear experts,

My company is preparing to upgrade its PI 7.0 (dual stack) version to 7.5. We are currently debating our installation options based on a critical interface that has been built using ccBPM (brief simplification can be found at the bottom of the thread). Our first option would be installing PO 7.5 (single stack), and build a BPM to substitute our old ccBPM solution, but we were considering simplifying this interface architecture in order to remove the need for a BPM solution which would result in a full PO installation. Our main goal is to keep our landscape as simple as possible.

Brief explanation of the interface:

1. SAP ECC start a async call starting ccBPM;
2. ccBPM executes a sync interface with an external web service;
3. After some transformations and validations, ccBPM starts a async interface routing to multiple abap proxy possibilities;
4. Return to step (2) while the external web service still has some data to be consumed;
5. At the end of ccBPM execution, it calls a RFC to inform that the processing has ended.

The minimal practical simplification for us would be:

1. SAP ECC start a sync request to PI wich route it to external web service
2. After PI receive the response, it should be able to do the following things:
   1. Start a async interface to ECC (taking advantage of all the proxy that have already been built*)
   2. Reply to the sync call of ECC passing some basic information of the message processed;

* Considering that the transformation of abap to java proxy has already been done, if a single stack installation has been chosen.

It is important to state that this external web service can return more than 100 different message types with completely distinct xsd, this is the reason for us to keep the PI to ECC async proxy call.

The main question is... is it possible to build such interface with a PI only installation? Both single stack and dual usage are acceptable for our basis team.

Thanks in advance.