There's an analogy that Ethereum is like a CPU, where BitShares DACs behave more like Application Specific ASICs. That prompts a question, why would you want a CPU to do what an application specific GPU can do better and with less overhead? I don't know, whether Ethereum ever might want to limit itself to what is not possible from Application Specific offerings rather than trying to reinvent them. For all the pretensions of doing Namecoin in 9 lines, for example, why would Ethereum want to do that? - There's no added value being on Ethereum, where there is however substantial added overhead.
In the case there are multiple chains: if you do set multiple 'CPU's running, then each Ethereum chain could be tasked with a unique complex problem; or set of problems relative to the size of storage and strain on any one chain. Other 'chains' could then be also BitShares or any other 'GPU'.