The ability to have more levels.

The game already has _SOME_ support for additional levels, so there is no need for the new tags.
VeteranCap= allows for more veterancy levels, but are of little use as the game doesn't know/can't do anything with them.
VeteranRatio= controls the amount of EXP needed to be promoted. Vet Level 1 = this x1, Vet Lvl 2 = this x2, so on.

But leaving these technicalities behind, I do like the idea of supporting further veterancy levels. Later CNCs added an extra level of veterancy (heroic) and there _may_ be people who would want this in their own mods, as a way to spread the bonuses units gain (instead of VeteranAbilities=EVERYTHING AND SELFHEAL).

An alternate implementation that falls within the scope of the original request could perhaps be:
-The game looks for a veterancy.shp, which if found would override the default veterancy icons for units, with the frame number corresponding to the veterancy level. Per-unit overrides will function the same way.
-Support Veteran[float].Abilities= to replace the old Veteran/EliteAbilities.
-Considering multi-weapons, it may be best to just have EliteWeaponX/Primary/etc, go into effect on the last allowed veterancy level.

Very smart additions EVA-251. It would work out pretty well but what if it could support a new weapon every level (if you wanted it to).

tags:
[UNIT]
Primary=Gun
ElitePrimary(or whatever that one is called)=GunE
Secondary=AAGun
Elitesecondary=AAGunE
3.primary=GunEE
3.secondary=AAGunEE

Have it so it goes up by numerals after the first 2.

I think transform-on-promotion logic in bug:179 and custom insignia in bug:454 will solve this.