In my opinion this could be the perfect compromise to make this class a little bit more appealing without imbalancing the macroclass comparison and I will tell you why.
According to what we know about tanks we should consider some main aspects other than Aggression, Ultimate Defense and Chain strike. Let's see how Eva's Templar compare with other 3 tanks
1 attack/debuff skills
2 aid/buff skills
3 Ultimate/Endgame skills
Let's analyze only skills they don't share with other tanks or they partially share:
1 Tribunal, Entangle, Arrest
Tribunal is probably the only way TK can actually deal some damage while giving a rather fair debuff, useful against high dps melee enemies. This skill is the parallel version of PK's Judgment which at the same damage output, is useful against the same kind of enemy. DA/PAL have instead Shield strike which gives no debuff but has an higher overall damage output and faster casting (1,58 seconds against 1,8 same cooldown)
Entangle is in my opinion a pretty good debuff against any kind of enemy. Same effect of DA's Hamstring just a bit slower casting but same cooldown. Useful sometimes in PVE too if you consider how fast TK is. This will give TK the best kiting result with the least effort.
Arrest is shared only with BD and SWS. This single target hold is actually pretty good when chasing an enemy since TK may have the best overall speed. Still a good skill to make a save when things go down fast. PAL has Mass Shackling which gives the same effect but AOE instead of single target (having a very slow cooldown)
2 Guard stance, Cubics, Aegis
Guard stance is the skill you don't want to underestimate when it comes tanking. This should always be on as it pretty much compare with DA/PAL Majesty. Its effect combined with Shield Mastery passive + Shield Fortress and Aegis + shield buffs we all know from supports, can make TK the best shield user of all tanks.
Cubics provide good stability as they cast aggro, hold, heal and sometimes a bit of damage. Overall defensive compared with PK's cubics, empowering the defensive status of TK.
Aegis (read guard stance)
3 Touch of Life, Eva's Protection
Touch of Life is one of the ultimate defensive skills which can give a great help in pvp to protect a DD or your healer. It can be used as an emergency heal. It doesn't compare well if you consider the damage of Touch of Death. PAL may benefit a bit more from this skill when you think about its other abilities.
Eva's Protection will give a great boost to pdef, mdef and speed of the entire party. Compared with Shield of sacrifice, it gives less defence but has no cost in terms of HP. The speed boost is actually pretty awesome imo.
Now if look at what Temple Knight is missing, we will see that he doesn't have major debuffs like Fear/Paralyze, major weakening skills like PK dot ones or major aid skills like Sacrifice.
Giving Temple Knight a stun that doesn't deal damage but cancels enemy target, may actually bring him a little bit up in the comparison chart while also diversifying him from the classic Shield Stun user.
TL;DR Temple knight may reveal to be the best kiter and shield user while also being the fastest tank. Giving it the old version of Shield Bash will make it more viable and enjoyable without breaking the game.