If Side Chains run adequately on say LTC for long enough to see some of the tail risks play out, and we figure out how to handle those, then I would see that as a beneficial outcome.

On the other hand, some of the pernicious effects may take a very long time to work out, but we'd see them on LTC well before we'd see them on BTC.  (Or even better some new coin designed with this as its purpose.)

Say for example, what happens when a SC becomes more valuable than its MC and stays more valuable?
What happens when it approaches this circumstance and it upsets the equilibrium (where it may become profitable to attack a SC with already sunk resource from merge mining ASICs that are funded through MC emission)?

These are economic circumstances that would be highly disruptive, but might not manifest for possibly many years after it were implemented.

The point here is that the big win should not be jeopardized for tertiary wins, (I think we agree on this at least), especially when the same thing can be accomplished without such jeopardy.  A Side Chain valuation may approach LTC valuation much more swiftly and there are enough economic analogs that the experience of handling it could be highly instructive.  We may learn that the currently proposed side chain structure isn't viable, or that it is.
We may get to see the reaction from the various regulatory entities that attempt to govern securitisation.   Throwing it onto Bitcoin without a proof of concept elsewhere would be a non-voluntary "taking" (also true for LTC).

At a minimum, this is the sort of thing that a responsible development team would engage.
I like the innovation.  I think it holds great promise.  It is not the big win, but it is a very significant win none the less if it works.

tl;dr
Fools rush in where angels fear to tread.