Here is a picture of Catachan guardsmen holding the line against a Tyranid attack, from the latest Codex.
Actually, who needs the guardsmen? Just give me all their vehicles!
This isn't to say I don't think all of that stuff is awesome. But the Imperial Guard have become a fully mechanized army. What happened to the Imperial Guard being the most diverse force in the Galaxy?
Here's a selection of what we have available to us, and their inspiration:
Catachans: Vietnam-era, i.e., Rambo.
Cadians: Generic modern-era soldier, ranging from World War II to modern.
Tallarn: Middle Eastern/World War II desert fighters.
Death Korps: World War I Europe
Valhallans: World War II Russian
What they do have in common is a 20th century aesthetic. For a while the Praetorians bucked the trend with their Zulu Wars inspiration, but GW has since renounced this "heresy" and swept them under the rug. Currently the Vostroyans are the only guardsmen that do not have a 20th Century aesthetic. Even the Mordians, while they fight in their dress uniforms, have a 20th century aesthetic.
While the Imperial Guard codex talks about less advanced guardsmen, those from feral, medieval, or pre-industrial worlds, for the most part they are rarely if ever seen on the battlefield. Indeed, GW does not provide any models for them. The door is left open if you want to convert some Warhammer miniatures, but that's it...
What about the Scottish Highlanders at Culloden? If IG players can paint camouflage patterns, surely we can paint plaid!
The Battle of Culloden (1746) by David MorierJust give those Jacobites some laspistols and they'd be good to go. For that matter, why not use some of those redcoats, too. Substitute lasguns for those muskets and you have some Imperial Guardsmen...
The point is, there are tons of really cool styles out there that would make some cool Imperial Guardsmen regiments.
I think the Vostroyans were an attempt at this, but the idea of Imperial Russians running around with tanks looks a bit absurd on its own, so they tried to give them a steampunk feel with their rebreathers and goggles.