Is it feasible to modify the contracts pallet to integrate it into a non-substrate rust-based blockchain? Say one that runs on Tendermint.
The contracts pallet is not written in a way that makes it easily integrate able into another code base. It is specifically written against FRAME (substrate's runtime authoring framework). However, there is no reason why it couldn't be decoupled. With some effort it could be restructured in a way to make it integrate able into different environments by making every I/O access abstract.
However, as there was no need for it nobody really is looking into that given that it would add a lot of complexity.