Here is the thread to check out:
From what I gather, the front panel is quite different, so you would need a new PCB and panel to upgrade. Of course you would also need all of the components that go on the board, and those are a big part of the expense (buttons, button caps, and encoders).
As someone who just finished a SeqV4, I am contemplating selling it so that I can have the fun of making another one.