Hey guys, Eric Martindale with Blockstream here.  The answer to your question is absolutely, yes!  It is definitely possible, and it would be very exciting to see BitShares as a sidechain.  If I recall correctly, there are many other related projects that would make equal sense as sidechains, too.

However, choosing to migrate from the existing model to a bonded sidechain is a different question.  While sidechains already exist in the wild (see the alpha sidechain if you're looking for something to prototype on top of), creating and configuring one isn't trivial (yet).  As part of the Elements Project, we're hoping to make this easier, but migrating any existing project to a sidechain will incur some amount of technical work.  In the case of BitShares, I would expect it to be significant – you'll want to make sure the benefits are worth the effort.

I'd be excited to have a conversation with Daniel or someone else from the BitShares team if they express any interest at all in pursuing this idea.  Obviously, I'm excited about it, because I think there is very clear value in doing so, but I'd want to make sure that sentiment is shared among those responsible for BitShares.

I, for one, think a world full of many interoperable blockchains is an exciting one!