The biggest hurdle you are going to run into is the bed. Specifically powering and controlling a larger bed heater. You cannot run any additional power through the Rambo board bed controller, so you will need to utilize some sort of relay or SSR / mosfet to control what will probably end up being an AC powered bed off its own power supply.
THe next biggest hurdle is increasing the frame size. There are a few projects here based off increasing the size of the taz, the main takeaway is that using smooth rods isn’t viable much beyond 300mm bed size, so you need to look at boxed rails or similar for strength. You also need a frame that can support a much longer printer. Making the components bigger means you need bigger motors to move them (NEMA 23 for the bed) and you run into issues like spring rate on the belts causing ringing, etc. It’s definitely doable, but it isn’t a quick or cheap process and there are significant technical issues to resolve.