I've just noticed that there hasn't been a lot of word on the visual upgrades for the units, like the ones for the marines (riot shield). In fact, the riot shield is the only one that I know is being made! :[ Are there going to be anymore visual upgrades?

Yes, I can confirm that some units get visual upgrades when you boost them through research.
Zerglings, Marines and Banelings are just some examples though, as there are other units that are getting a visual upgrade.

For example, Battlecruisers have the ability to choose between three specializations:
- Defensive Matrix (a shield that absorbs damage)
- Missile Pods (Air to Air AoE damage)
- Yamato Cannon (honestly, do I need to introduce this one? :) )
Each one of these specializations changes the graphic of the battlecruisers, thus making it easily recognizable.
Just to clarify things up: you can only have one specialization per Battlecruiser, and once you choose you cannot switch to another one.

But not only units are affected by this visual upgrades, even buildings are being visually upgraded.
Let's talk about Bunkers: when the NeoSteel Frame upgrade is completed (+2 cargo space) the bunker actually gets bigger and taller.