In terms of Infantry gear, The Only real Step above what our current troops field for armour Is Actual Power armour. The form it will take is Probably up to decision, in specifics of the suit, whether it Cleaves closer to SoB standard, or a Vottan heavy plate knock off, its highly likely that it will be SOME form of PA for our dudes, Or even multiple variants.
More In contention are standard line infantry firearms.
The Lasgun is a Logistical Miracle, And for the imperium is a god send. But we aren't exactly at the size were the logistical Miracle of the lasgun because a necessity. The hotshot lasgun is good, and will probably never be fully taken out of the armoury because of its ease of supply and recharging making it a great weapon for when logistics get bare.
Past that, The Imperium standard Firearms actually has a wide variety we can pull from, without looking at any other faction.
The Volkite was replaced with the bolter, More out of how hard it was to build then a real Advantage. If we can recreate the volkite, It is noted as a great weapon, Capable of Deflagrating organic targets and seemingly good against Ceramite plate as well. At the very least I can't fin anything that says it does worse.
The Bolter is actually a Fully reasonable weapon for our forces to move up to if we get Full PA. It IS the standard for SoB and Space marines for a reason. The shell is a bit complicated, but the gun itself and the shells can be built with decent logistical ease. Its not the BEST verses heavily armoured targets such as space marine's, but its is the absolute of Post-pen Damage. In a universe with creatures like daemons, Orks and Tyranids, All of whom can Take an insane amount of damage and keep moving, that trait is down right invaluable. Combine that with The Fact that A Bolter shell is a fairly versatile Platform, Its a Great choice for a standardized weapon.
Moving into weaponry a little more out of their, the Mechanicuses skittari use a fairly wide arsenal, but the two "standard" infantry arm is the Galvanic Rifle and the radium... The skitari also have a ton of other weird weapons' that can replace this, but i'll look at this for now. The galvanic rifle is... Fucking weird. It looks like a flintlock rifle, which I fucking love the aesthetic. The bullet this thing fires is weird. Its a long range sniper weapon that fires a Bullet... the apparently turns all of the targets potential energy into an electrical explosion to kill the target. Don't even know how thats possible, can't even analyse this shit, but it looks like a Snipers weapin, compared to the other Skitarri standard gun... The radium carbide that kills its wielder with radiation even as it fries the target. Jesus mechnicus, I can't use any of this!
EDIT: Expanding on "Weird shit the mechanicus just HAS" A Possible contender for mainline infantry gun is the Arc line of weaponry. Not much lore, So most of it is based off visuals and Tabletop stats, which are not a good thing to go off, but they Fuck Hard, Both Visually, and in use. An Arc pistol can apparently not just stop an orks heart, but punch it backwards out of force. The main drawback is the fact that the weapons are seemingly rare, Incredibly hard to make and created from something called "permaCapacitors" Shipped straight from mars, which if the name is even half correct is a raised Eyebrow from me. This isn't even getting into the weird Heavy weapons that factions just has, this is all infantry scale stuff
Vottan are interesting, because their gear can basically be summed up as Space marine/Imperium ++. They have really good Bolter's, but more interestingly for us, They show that Las guns can go past where we are now with something called Hylas, Which is basically just Super-las guns that Fire incredibly fast, hit incredibly hard, and Have a Extremely Long range, Showing that the Hotshot Lasgun CAN be Improved even farther. The Vottan weapons are Better then we can do, but It helps show where we CAN go.
Basically, I am very interested In seeing what our options are, because we have plenty of places where this cane go.