Merge data, dataflows from 2 BW systems into one to reduce cost and one way of working

Hello BW gurus,

I have a question here in my current project we are asked to merge data from 2 BW system to one.

This basis for this is there each  BW system has their own R3 systems.

First they have now started to migrate data from ECC1 system to ECC2 system using DSM tooling and mapping tables to align to one way of working.

Only open items are migrated from ECC1 to ECC2.

BW1 system is connected to ECC1 and BW2 with ECC2.

Now they want to merge BW1 to BW2.

In BW2 historical data from BW1 is needed.Data for open items from BW1 will come from ECC2 as they are being migrated.

What should be the approach to migrate the historical data from BW1 to BW2.

There can be several scenarios :

1)BW Objects migration

2)Data migration

3)How to deal with common object names used in both systems for DSO and cubes where the data flows in both systems are same?

4)How to deal with common MD info objects (eg:0customer,0vendor) and also if the cutomer numbers in both system are same but with different description and vice versa.

5)How to deal with same kind of transaction data?

I went through many other discussions on the same topic but there it is mentioned to concatenate the 0logsys or sourcesytem in the dataflows where common master is used but creating z objects a copy of 0 objects like 0customer etc.

In these cases if I need to do this to existing 0customer object in that case it would mean deleting data from all flows where 0customer is used if I want to add sourcesytem the compounding which is not favourable.or in case of creating z objects of existing MD IO then add sourcesytem compounding in those cases also it would mean I have to use the new zobjects in all those DSO/Cubes/MP/Queries in place of original object which is also a lot of effort and also load data into it.

This can be done for DSO and cube flows but not MD IO.

Please suggest some good approaches /ways to the above criterias I have mentioned.

System speccification: Currently we are on BW 7.4 version but with the merge we cannot go on Hana due to cost control so we need to use the BW system only.