Pandects for Armor and Weapon proficiency: One pandect grants two "ranks" going from light -> medium -> heavy armor or simple -> martial -> exotic weapons respectively. Or just grant the two last ones in the chains for simplicity.
I can think of barbarians, rogues, shifters, palemasters, dragon disciples who could make use of the armor proficiency, while additional weapon choices might be useful to druids, monks, rogues, shadowdancers, shifters, some odd wm/rdds, staffmasters or any tank that would like to add some more exotic mega damage weapons to his arsenal. It might also open the possibility of adding more special weapons (like the machine spear or the tear morning star) as exotic weapons.
Problem I see is limited bonus for the Weapon Proficiency feats as you need them before you take WF and w/o WF there is limited reason to want or need many of the Weapon Proficiencies. I can see the Armor one being useful much like how the Shield one is useful but likely to a lesser degree.
I don't think the point of a pandect is to free up a feat you'd take in the normal level progression, it's rather some perk that gets added on top what you've already got. I wouldn't suggest to read a weapon prof pandect so you can take weapon foci afterwards, but rather to broaden the weapon selection you can actually equip. To wield the tear morning star you need simple weapon prof, a feat druids, monks, wizards and shifters often don't get as part of their class feats. Similar with the machine spear, which can't be used by some wizards, rogues and monks.
On my staffmaster for example I'd rather use a pandect for simple weapon prof to wield morning stars and spears instead of a pandect that improves sneak attack by 2d6 or increases my elemental resists. Same with my shifter(s); not really because of the special weapons, but rather to increase the selection of (megadamage) weapons I can use. Especially since druids and shifters can't select other weapon prof feats during level progression.
I understand that a weapon prof pandect might not be as sought after as a disarm (tanks with high ab), shield (pure arcane casters and rogues) or spell resistance (anyone with innate sr) pandects. All of these pandects are useful only to certain builds though and completely worthless to most others...just as a pandects for weapon or armor prof.