I could put in something like the losing one armor proficiency gains you a bonus feat, losing a second gains you an extra special ability (probably from a separate list than the normal one, at least much more limited), and if you lost your third it would net you...i'm not sure, something though.
For the weapons, if you gave up all martial proficiency you would gain a bonus feat.
something like that would let specialization be easier if you really wanted to lose your proficiencies. one stipulation would be though that these can only be taken at character level 1, to avoid a quick dip from someone to gain big bonuses. then again, i could make it a trade during your first few levels. being able to lose heavy armor proficiency or martial weapon at 1st, then medium armor if you lost heavy armor, or martial weapon if you still had it at 2nd, then 3rd level you could chose to lose light armor if you lost medium.
that would make anyone wanting to dip into this at least invest a few levels, and if you gave up the martial weapon proficiency for the extras, you can't gain it again.
that's kind of one big ramble, but take from it what you will.