The only change I think is required sometime in the future is some form of buff to the Battlecruiser. I see all other units in high-level tournaments on a regular basis right now ( Which is freaking amazing! ). My wish is mostly design based but I think that a viable Battlecruiser could help balance the lategame vs both Protoss and Zerg. I don't think Terran is massively underpowered lategame ( In terms of available power ) right now but they do require more effort imo ( Just play like Maru ).
I have riddled this post with "imo" since that all that it is. I love this game and as with everyone in here I just want to help it improve even more from what is already the best game in the world! Cheers!