Shen Rework (Minimalist)
I think if you wanted to update Shen to be competitive in the current meta, while changing as little as possible, this would be the way to do it.
Ki-Strike
Ki-Strike's cooldown is reduced by one second at levels 6, 11, and 16. Energy restored is 20 at all levels.
THOUGHTS: This would help Shen to scale better into the late game, which he doesn't do at all right now. The change to energy restored goes with my other suggested changes.
Vorpal Blade
Increase base damage: 60/120/180/240/300(+60%AP)
Increase heal ammount: 10/18/26/34/42 (+1.5% of Shen's max health) Instant heal is the same...
Reduce energy cost at later levels: 60/55/50/45/40 ---or--- 65/60/55/50/45
THOUGHTS: Simply up the base damage and heal just a LITTLE bit. Typically, Shen builds HP and resist. So since you don't build lots of AP on him (gimmiky) having a slightly higher base damage and heal, would help against all the high damage/ high sustain champs, without making him oppressive. Also, Shen is currently the only ninja with skills that don't go down in energy cost... Isn't he the leader or something? Why does he gain 1/3rd health back when he kills something with it... He already lost the ability to hit it more than once, and he cant share it with allies... Why punish him further?
Feint
Shield base is reduced slightly, but scales with HP: 80/110/140/170/200(+15% Shen's Bonus HP)(+50%AP)
Reduce energy costs at later levels: 65/60/55/50/45
THOUGHTS: Better Shield means more cost early. Shen is a tank, and his current shield is worthless. This would make it at least a decent shield. Higher starting costs will contribute to still having some energy issues early.
Shadow Dash
Revert nerf to hit box size.
Scale the energy costs down: 120/110/100/90/80
Scale the taunt duration. 1/1.25/1.5/1.75/2 seconds.
THOUGHTS: As a tank, this is his ONLY form of CC and there are several other taunts out there that are WAY better. This ups its power a small amount, gives early energy issues, and lets him scale to be more threatening late game.
Stand United
Reduce cooldown: 200/160/120
THOUGHTS: Shen's ult is powerful, but not nearly as powerful since the introduction of the TP summoner spell. It destroyed his most unique ability. (They TP'd Shen's house, see what I did there?) Simply allowing it to be up more would make a small window where his ult is up but the opponent's tp is down after they use it to follow Shen the first time.
This is my minimalist change list: Thoughts?