one threat vector that i feel is underappreciated is reputation of Bitcoin related to the insinuation that the sidechain coins are just as valuable. they arent.
Someone receiving drivechain1 sidechain coins need to withdraw/move to btc (3+ months) before spending in a normal transaction, or depositing into drivechain2 sidechain.
that lengthy withdraw process to btc, and incompatibility between sidechains is a form of encumberance and the value of that in a drivechain sidechain may be discounted accordingly.
people who experience bitcoin first by receiving in a drivechsib sidechain will understandably be upset about the lengthy time they need to commit to in order to transact on chain to even move those funds to traditional lightning channels for Bitcoin. this can cause reputational harm to bitcoin as it will be (has been) lumped together (affinity grift)
the faster way out will be some service offering to setup a swap for a fee. peer to peer may be viable, but in either event the liquidity of such trades will be low.