I understand bigger body types are able to use heavier weapons, but is weapon usage dependent on class choice at all? For instance, will a light soldier have access to a few more soldier-like weapons than a light operative? I think it makes sense for weapons to be decided by both class and body type, but I can also see this being frustrating in some ways.

No, any class can use any weapon. It's all dependant on the bodytype.

The only thing might be that soldier get access to a few more diffrent grenades I believe.

Yes, Soldiers do have a larger variety of grenades.
Engineers have turrets.

There are class-specific abilities, but not weapons. This allows you to quickly switch classes without having to change your weapon-loadout as well.

It is traditionally makes sense for class to resrict weapon choice. Wedgwood even discusses it in an interview, for example engineers always get shotguns. Its a nice change from the average FPS.

Agreed, it is a nice change. More focus will be put on improving your playing ability of a specific class based on that class' roles and abilities, rather than solely picking a class because you think they have the best weapons. This just makes me that more excited for Brink...

I think it will also help with teamwork, indirectly. You wont have a team full of soldiers because everyone wants an assault rifles, or have a team with no medics due to medics having the worst weapons.

Would save certain games from everyone playing the sniper or recon class.

Like BFBC2. *shudders*

0 points in the recon class and proud of it!