I basically have a suggestion for bettering the Seal system, which aims at restoring some of the interactivity between the Seals and other existing abilities. Part of the suggestion relies on tweaking a few existing abilities, talents, and even a few Hand spells along the way, but I'm confident it would all fit together nicely.
Firstly, the current Seal system provides minimal interaction with other abilities. It primarily benefits auto-attacks and secondarily benefits melee strikes such as Crusader Strike and Hammer of the Righteous, and in a distant third it benefits Divine Storm (for Ret only) and Judgement.
A fine suggestion to bring back some interaction between Seals and shared abilities like Crusader Strike, Hammer of the Righteous and Divine Storm in addition to Auto-Attacks. You could have something on the order of Seal of Truth putting the Censure DoT on any target hit by CS, HotR and DS. Seal of Righteous would do essentially the same thing it does now by dealing extra upfront damage on CS, HotR and DS. Seal of Justice would apply the Snare effect on CS, HotR and DS. And, finally Seal of Insight would heal and the Paladin with CS, but could be Glyphed to heal any target around the target with HotR and DS.
This would seem ok, but then you'd run into the same issue where people wouldn't bother much with Seal of Righteousness because Seal of Truth could build up to dealing so much more damage. Perhaps this might end with the removal of Seal of Righteousness.
The better suggestion I have would be to put the interaction back into Judgement along with the ordinary melee attacks (Auto-Attacks, CS, HotR, and DS). Seal of Truth applies Censure DoT with Judgement (as it does now). Seal of Righteousness damages the target and all targets around that target with Judgement. Seal of Justice applies the snaring effect on Judgement. And, Seal of Insight heals the Paladin on Judgement (as it used to).
One glaring issue brought up is that Snare on Judgement is handled by Burden of Guilt. And so, some kind of similar ability to compensate for it would be needed. I would introduce:
Hand of Justice -
Places a Hand on an Enemy target, reducing their movement speed by 20% every second for 6 sec. Replaces Hand of Freedom.
It performs a similar function to Burden of Guilt and seems a more thought provoking decision on how you want to control enemies; particularly for Ret who would have access to both, although Ret would need to weigh taking this if it means giving up HoF. This may necessitate the two sharing an internal diminishing return, such that a target already effected by Seal of Justice would only suffer 3 sec from the Hand of Justice buff.
The second anticipated issue is that Seal of Righteousness, by mimicking the effect of Holy Prism might require replacing that talent all together. I would agree; particularly considering the healing effect from Holy Prism could be mimicked by adding a Glyph to Seal of Insight, such that the healing dispersed to targets around the target (probably for a hefty mana increase to 25% base mana to compensate). But, what to put in its place? I would say this is the better place for Blinding Light:
Blinding Light -
Emits a dazzling light in all directions, blinding enemies within 10 yards, causing them to be knocked down for 3 sec and take X damage over 6 sec.
Disorienting them and having them take damage wouldn't make much sense unless you created Repent-style exceptions to the Censure DoT and Dazzling Light DoT. The damage over time from Blazing Light will need to be in line with Execution Sentence and Light's Hammer to make it a viable choice.
The definitely seems the best means to implement Seal interactions back into the game that stay meaningful to all three specs and trade out similar talents for viable replacements.
EDIT: Edited for clarity that Judgement would be gaining more interaction with Seals in addition to the existing melee attacks.