remember, the scBTC will start out below the BTC when first introduced. who knows, it could be close to zero, or may quickly elevate just below the BTC price. then the speculator launches the attack by pumping BTC thru the peg. at the same time, he embarks on a forum blitz saying how great the SC is and how it will take over. since these scBTC will be traded on an open exchange, the market will view a rising #scBTC and a rising price on the SC as validation of the innovation, just like you did when questioned. if i saw that happening, i'd move a large chunk of my BTC into scBTC immediately b/c i also know there's a risk free put in place. especially if the SC has been functioning bug free for a number of months. as more and more ppl make the same conclusion, the scBTC will rise even more dragging up the BTC price as arbitration sets in. but astute investors will see that the scBTC is leading the BTC price or at least rising faster. this would indicate that the SC may take over. as that happens, cold wallet hodlers are placed into a bind. either follow or risk losing value as i think miners will also make the switch to the SC b/c their fees and block rewards paid in scBTC are higher. once enough of this happens in a mass transition, i think it's logical to believe the Bitcoin will become the MM'd chain and the SC the MC. this will occur if the added innovation is valid, say like perfect anonymity.
so the incentive is to move first or risk losing value by having the MC become obsoleted.
the problem is even worse when you have an innovation that is controversial; like faster confirmation times. a speculator will pump the price until others follow, and then dump, whipsawing everybody.
that is not an incentive to create a speculative attack. basically you just reiterated your mass exodus scenario but you didn't prove why someone would want to precipitate this exodus and how it would benefit them (other than the obvious "don't be left holding the bag")
the speculator would be converting to scBTC when the price was low. as he continues to pump across the peg, the scBTC price will rise. as the SC attracts more conversion of BTC to scBTC, the price will rise even more. as miners and nodes switch to the SC, price should rise even more. at some point the price of BTC will drop below that of scBTC b/c the MC will become the MM'd one and therefore less secure. the last ones out of the MC may get blocked by 51% attacks or their SPV proof fees might rise to very high levels.
in the scenario where the innovation is invalid and the MC is destined to stay the MC, he could just create a pump and dump of scBTC.