As this blogger has said elsewhere the history of blockchain databases is probably fated to mirror the history of relational databases.
They both started life with dismal transaction rates which in the latter case actually led to the development of dedicated relational database machines. In both technologies the different vendors have done their utmost to prevent interoperability between their products and lock customers into their own product. In the relational world developments like the XA transaction standard eventually opened it up. It seems the same may now be happening in the blockchain world as at last there are efforts to establish standards to support interoperability between different vendor's blockchains. Will there ever be standards to support transactions that span different vendor's blockchains? This blogger is not qualified to know if that is even theoretically possible.