Cuirassiers, kind of a big deal.
Most nations fielded cuirassiers, or other armored cavalry to some extent during the Napoleonic Wars.
My concern is whether or not these guys, often perceived as elites, will get the "oomf" that they deserve. Take the current leading game for Napoleonic Wars, the DLC for Mount and Blade; cuirasses and helmets are like paper. Now, of course, close range musket fire should punch through armor; but what of pistols, bayonets, swords, bludgeons, shrapnel, or even the stray musket shot at great range? Hell, even the tall leather cavalry boots offered a bit of protection to the exposed legs. Body armor and helmets still had niche effectiveness, which explains why it was still worn by heavy cavalry units even into the first World War, so I really hope that this game adequately represents that.
Of course, there is the concern of balance, but I wouldn't think it too hard. Bearing armor is taxing, and as such a cuirassier should not be able to catch up with a hussar. And, should a cuirassier find themselves dismounted, they would no doubt be slowed to a comparable crawl. Barring that, one could simply limit the amount of available armored cavalry, after all; steel armor and a well-bred horse capable of supporting the extra weight is expensive.
Just hoping the last of the knights in shining armor get the attention they deserve.