The Amalgam universe was deliberately short lived and was founded as a marketing ploy, however did serve as a rather good branch between companies. I see three major options:
1)Marvel or DC buy DC or Marvel out, and merge the universes with the Amalgam Characters.
2)Amalgam proves to be more popular, leading to further crossovers. Whilst not a continues series, every few years Marvel and DC unite to tell more Amalgam stories. Basically DC/Marvel: All Access and Unlimited Access are published under Amalgam and become more reoccurring.
3)Shared characters leads to the need for a third imprint to escape legal hell without either company surrendering those charterers, although this needs these charterers to have a large demand.