I don’t know if I’m the only one who came to this conclusion, but I think in the new progression system, gun upgrades should be separated from squad upgrades. Otherwise we will end up being forced to research through all previous guns, before able to research the last one. Also, I think that current system is to arcady and straightforward - no choice, no logic, no real changes. And its quite boring to research first base gun, that sniper variant, than GL variant, while it is the same gun.
I suggest next system: in a tech tree each piece of equipment has its own small research subtree.
For vehicles modifications could be copied straightforward from WT (except ammo and consumables). For guns it will be modifications, listed below.

Logic is that player researches new modifications for playing with that equipment and after that buys modifications for each piece individually (for vehicles mods bought only once).
Gun modifications:
Rank I:
Gun cleaning - speeds up all manipulations with charging handle (or bolt for BAs) by 15%
Sight calibration - lowers dispersion by 8%
Stock calibration - speeds up ADS by 10%
Lower modification cost - reduces mod cost by 10%
Rank II:
Magazine reloading - Semi-auto rifles starts using magazines instead of stripper clips. Drawback - less reserve ammo. (For example - SVT-40 has 10+30 rounds by default, with this upgrade - 10+20, but this 20 in 2 mags, with ammo pouches both types can be increased)
New barrel - further lowers dispersion by 10%
Grip adjustment - lowers recoil by 10%
Optics - guns with sniper variants has this modification to turn them into sniper rifle (instead of having separate weapon). Guns with no non-sniper variants goes with this mode researched by default.
Grenade launcher - works same as optics. You researched it, you attached it, you reseived rifle with GL.
Sights modification - turns diopters and closed sights into halfrings.
Lower modification cost II - further reduces mod cost by 15%
Rank III:
Variants: allows to buy gun varians. SVT-38 → SVT-40, MP38 → MP40, PPD38 → PPD40, Kar98k → Kriegsmodell. Some variants are slightly better (SVT-40), while others are just cheaper (MP40, Kriegsmodell)
Drum mags: changes stick mags to drums, increases BR
Lighter bolt - ROF +10%, recoil +10%
Magazine catch adjustment - increases speed of inserting/extracting mag by 20%
Lower modification cost III - further reduces mod cost by 20%
How to get to this new system:
Researched upgrades turns into free XP for this gun.
Bought upgrades refunded in bronze orders, as gun/vehicle was upgraded from +1