Cap'n Kobold
Hero
I don't think that it would push most warforged into light armour-based classes. Most light-armour wearers will start with a dex bonus higher than +2, and games very rarely get to the point where the proficiency bonus is going to be higher than dex.That is... a really interesting take. It would have the impact of reducing the power/draw of the Dex based characters. The one issue I see is that you would see a lot of warforged with a preference for light armor, which thematically doesn't make much sense from my perspective.
You will get higher level warforged wearing less armour as their own plating develops to be better and better, but I can see it encouraging heavier-armour wearing actual classes, because they tend to have less of a use for dex in other aspects of the class.