I was curious about this archtype, because as-written it is a ridiculously powerful set of abilities.
The flaw, as stated is the lack of int to hit and using the half BAB progression.
The build I ended up coming up with caps at lvl 11, but is perfectly functional every step of the way.
Key points:
3 levels of Magus, taking arcane accuracy as magus arcana
rest white haired witch
Elements patron for shocking grasp
King Crab familier for +2 grapple
Magical lineage (shocking grasp) combined with intensify spell feat, allowing for lvl 1 shocking grasp up to 10d6 damage
Weapon finesse + combat reflexes and make dex your secondary stat
then just take Grapple feats and maybe extra arcane pool
Ring of wizardry 1 as soon as possible
This gives you a large number of intensified shocking grasps to spellstrike with your hair with, granting the +4 to hit if they're wearing metal. Then the extra +int to hit when you need it from the arcane pool.
Magus also gives you access to true-strike, that can be spell-combat casted for an equiv of +18 to hit when you really need to make the hit to get the grapple.
Once you have the money, get a lvl 12+ wizard (pref lvl 20 if your setting allows) to cast Greater magic fang and permenancy it on you for another +3-5 hit/damage (total cost 9100 for 20th level to cast it)
So if anyone moves within your increasingly long reach, you get your AoO, which you can trip or grapple them with.
The final lvl 11 build I made around this is +16 to hit, +24 when using one of my 9 arcane pool for accuracy, and +28 if they're wearing metal. With 15 intensified shocking grasps I can reliably do 11d6+13 damage with my attacks, and then grapple with a +20 CMB, maintaining the grapple as a move action allowing me to continue to cast spells as normal while doing 1d6+13 constrict damage to that target each round and a 35 CMD to break free.
Edit:
figured I'd post the final build:
White Haired Witch/Magus build
It's in my relative shorthand for making a character, I hope it's understandable.
In conclusion though, I agree that adding int instead of str to hit would make this ability a lot more intuitive to make a character around, I made the above character as a thought experiment to see if I could make it work. The character concept behind it is based on japanese combat anime, as that's a great way to roll with the hair being your weapon.
In addition I would rule that you get int for all of the maneuver checks within the grapple by your hair. for the same reason I'd rule that you can't grapple more than one person at the same time with your hair.
