This is very cool but it uses the term trustless to describe something that isn't. An important feature of this protocol is that the liquidity provider is not forced to call the contract they promise to call on your behalf.

If they don't, it falls back to a relatively decent failure state where you get enough rbtc to call the contact yourself, after a waiting period of several hours. But this means you lost your actual bitcoins and didn't get the function call you wanted, instead you got lousy rbtc after a waiting period. Since you can pay for a thing and not (quite) get it, this means the liquidity providers can (slightly) rip you off.

Now, even that ripoff scenario isn't quite so bad, because you can probably get the function call you wanted using the rbtc you got to pay the gas fees to make the call yourself. But not if fees shot upward during the waiting period. So it's unlikely but you can be permanently ripped off by liquidity providers, because you might never get the function call you paid for, even after waiting.

Even that ripoff scenario is not quite as bad as it sounds, because you can probably get an almost complete refund on the bitcoins you originally paid by selling the rbtc you got, or by using rootstock's standard peg out mechanism. But either of those requires trusting the rootstock federation, as does making the function call you originally paid for. The rootstock federation can pull the rug at any point between the moment you make the function call and the moment the function call either completes or you get your refund. So you're trusting them not to do that the entire time.

Therefore this protocol is not trustless, but even so, it's great.