If such a fusion happed it could resemble the merger between Oracle and BEA in January 2008. It also was two companies with the same product suite for the middle layer. Oracle then had select which of the products future development should happen on. For the integration part the BEA product was selected, so all consultants had to learn the new product.
SAP did a similarly integration with Business Objects, which from the side as given a lot of new products or rebranded products. For someone who has not worked with BI the integration of two products happened limited problems. From what I have heard it was the frontend from Business Objects and the backend from SAP BI, which was developed as a product, so a new best of breed application was created.
But Tibco has more than just one area of products they have complementary product whole Netweaver suite. For the integration/SOA part I have heard that Tibco should have some better products in some areas and the portal probably does not match how SAP has created the portal. Come to think of the J2ee stack it was also purchased from a company that I have forgotten. But that was on a time when SAP did not have the java stack.
Dennis Howlett says that SAP have to watch Software AG. And that Tibco’s Silver cloud platform could profit SAP.
If the acquisition is approved, then it would be interesting to see what that mean for customers, SAP and partners.