The firmware in Solo, and in the gimble, and in the controller, as well as the version of the app, can all be upgraded. Many hardware mods are possible; fans of each will enthuse about them in replies below. I've only done the improved 3DR GPS Shield mod and replaced the props with Master Airscrew props, both of which I highly recommend.
Here ya go mate Kinakailangan ang Pagtiyak sa Seguridad (I have no idea what this says but trust me, it's a link to the FB page)
Solo Mod Club on Facebook. Use the search bar