Really happy to hear Streamline is calming! <3
Those sound like some good suggestions! However all development effort on this project is currently being directed to Jetstream (http://jetstreamgame.com/), our spiritual successor to Streamline. Besides looking better, having much better audio and other polish changes, Jetstream has quite a few new mechanics, while removing the clunky two-player mode you're referring to (it was a nice experiment, but I agree - it's not as good). We're current working on a procedural generation mode for Jetstream and will be putting out an update with that, as well as bringing it to mobile platforms.
I'd love to also have some sort of level editor, but alas that tends to be an expensive feature to do. We have an internal editor, but it would be a lot of work to get that remotely acceptable for public consumption. Jetstream's procedural levels will be structured a bit differently, so it'll be a bit easier to share them in some ways - think more like groups of daily levels where everyone in the world gets the same set. We're working hard to get that done soon :)
Thanks for playing and your feedback!