This post contains what I feel would be a way to address several issues that we paladins currently have. This is my take on how Blizz can be rid of intellect plate; something they've been trying to do for years, rework paladin tanking to the new model; having to use your resource to now get murdered, and to fix the chunkiness and RNG of retribution's rotation.
Have fun with my ramblings.
Paladin mana will be removed entirely and replaced with an improved holy power system. All paladins will have 10 charges of holy power and will begin a fight with none. The powers a paladin uses will build holy power and others will use it. An example for each will be provided in separate sections below. The entire system is supposed to feel somewhat like the opposite of a warrior's rage bar, constantly fighting to keep your power somewhat full at all times.
Abilities that currently use holy power (Word of Glory, Templar's Verdict, etc) will now require 3 holy power to cast, and will always consume 3 holy power. Additionally these powers will be significantly increased, making them attractive to use, despite their rather large cost. This will allow paladins to split their holy power usage easily and hopefully take some of the "mathiness" of the system.
Protection paladins will be changed to use their holy power to protect and heal themselves. Protection "builders" would include Hammer of the Righteous and Crusader Strike. Protection "expenders" would include a series of reworked powers, many of which will grant the paladin buffs to his defensive stats. These will make the paladin more defensive than current when he is able to maintain them, but less when he cannot, forcing a paladin to spend his resource to stay alive. His mastery would be reworked to cause these effects to be more potent, allowing him the chance to decide to stack mastery if he is more skilled, but stack normal defensive stats while still learning his class.
Retribution paladins will be changed to use holy power in a constant balancing act. Retribution "builders" will include Crusader Strike and Judgment. For a retribution paladin Crusader Strike will generate two holy power, allowing them to build faster and stay up faster than protection paladins. Retribution paladins will use their holy power to perform strong weapon strikes, including several new powers. Retribution paladins will focus on using the current set of powers that already consume holy power, meaning that building to sets of three holy power will be important for them. Additionally to deal with retribution's current chunkiness and heavy RNG reliance their mastery is also getting an overhaul. Their new mastery will replace the current Inquisition buff, which many paladins have complained about, this new mastery will increase the amount of damage retribution's powers will do based on the number of charges of holy power the paladin has, forcing them to strike a constant balance between spending and building holy power.
Holy paladins will gain spell power, rather than attack power, from all sources, much like an enhancement shaman. The transfer of power will be complete, but will only occur on "bonus" attack power, so a holy paladin will still have their base strength to swing with. Holy's "builders" will be Holy Shock, which will generate two holy power charges, and Holy Light, which will generate one. Their "expenders" will be Flash of Light and Divine Light, which will cost two and one holy power each. This will force holy paladins to strike up a balance between using their less effective heals and their more powerful ones. They will have a passive that, in addition to causing their attack power to convert into spell power, will cause their holy power supply to "fade" or "darken" as the fight continues. Once a holy power has "darkened" it will not be able to be charged by any normal means. This will occur every 30 seconds, causing them to "oom" after about five minutes of fighting. The current paladin mana cooldowns will instead restore "darkened" charges of holy power. Their "spirit" stat will be a redesigned mastery which will increase the amount of time that a charge takes to "darken" which will effectively allow them to heal for longer. This will also paladins to expend itemization points on staying in a fight longer, just as other healers need to do now.