Great callouts, I definitely get your concern around block sharing--that feature does exist currently in Warp but it is completely opt in on a per command basis (we never collect any command output without the user opting into it first). The way this works is that if you explicitly click "Share" by right clicking on a block, we will send the contents to our server and generate a link for you. A block can also be unshared at any point to completely delete a block from our server.
Regarding the cross-platform piece, the plan is absolutely to support different platforms. In fact we've built our own cross-platform UI framework to help us with this endeavor which you can read about here: https://www.warp.dev/blog/how-warp-works. We chose Metal to start because the Metal debugging tools in Xcode are excellent, allowing us to inspect texture resources and easily measure important metrics like frame rate and GPU memory size. Thankfully, because our graphics code is decoupled from our UI framework, porting the graphics piece of the UI framework essentially mounts to porting over a few hundred lines of shader code, which shouldn't be too difficult.
Regarding the cross-platform piece, the plan is absolutely to support different platforms. In fact we've built our own cross-platform UI framework to help us with this endeavor which you can read about here: https://www.warp.dev/blog/how-warp-works. We chose Metal to start because the Metal debugging tools in Xcode are excellent, allowing us to inspect texture resources and easily measure important metrics like frame rate and GPU memory size. Thankfully, because our graphics code is decoupled from our UI framework, porting the graphics piece of the UI framework essentially mounts to porting over a few hundred lines of shader code, which shouldn't be too difficult.