I can't wait for the multitude of sidechain forks that all compete with each other. Sidechains themselves require incentives to operate securely, such as fees and the continued security of the Bitcoin network, so I'd guess we'll start to see a lot of the same issues in sidechain space as we do in altchain space. I really don't think there's any difference between the two. You can also issue your own assets already on Bitcoin (e.g. coinprism, counterparty), so the notion of token issuance for use in general scamming will surely appear on sidechains as well. You can't out-technology human speculation in finance.
There is no speculation incentive because all investments are denominated in BTC. Thus this will force consolidation. Unless there are revenue models and/or dividends for side chains.
Ah... just like all alt coins are merge mined with Bitcoin to support the entire network hash rate? After Elements adds explicit tokenization it'll be easy for anyone to make a sidechain fork and issue "Sidechain Funbux" on their fork, pre-sale them, etc. Bilateral two-way peg also means that Bitcoin might inadvertently end up supporting a number of pre-existing alt. coins anyway; especially since we can now explicitly tokenize them in a 1:1 peg on the elements sidechain and transfer them there.
You can change the tech, but you can't change the underlying issue.