I dont know if Mearls and co. look the work of 3PP sometime, but I'm positive that they could find inspiration for a great martial support class that fits the power level of 5e by mixing features from AiME Scholar and Warden to create a base class that uses its wits to influence the ebbs and flows of the battle, while being wise enough to avoid them first. Both class are great take on spell-less healers/support that use 5e mechanics; they are just a little underpowered in a regular game where fullcaster are a thing.
Warden
1d8, medium armor + shield, martial weapons, save in Wis and Str
lvl1: Wounds Binding: Healing Die pool (on short rest), Watchfulness: Investigation test in a region to gather a all rumors, Momentum Die (as bard, 1d6 lvl1, 1d8 lvl11, 1d10 lvl 17), on Long Rest, 1+Int/day)
lvl2: Field Triage: Gain prof. in Medicine and Healers Kit, if already have it, double.
lvl3: Archetype Feature
lvl4: ASI
lvl5: Extra attack
lvl6: Battle Harmony: as a bonus action when Attacking OR Using an action to heal an ally, the warden can spend a Momentum Die to let an ally make an attack, adding the die to attack)
lvl7: Archetype feature
lvl8: ASI
lvl9: Stall tactic: 1/Short rest, when Initiative is rolled, enemy musk make a Int check against 10+your Insight skill or receive a - Int penalty to Initiative.
lvl 10: Find a Way: Allies within 30 have advantage on survival, perception and investigation check to navigate or find hidden features.
lvl 11: Archetype Feature
lvl 12: ASI
lvl13: Hidden resources: 1/day you or an ally can use an expanded ability that's recovered on long rest one more time.
lvl 14: Unto the Breach: When you or an ally roll a nat 20, choose an ally within 30, he receives 1 free Momentum Dice.
Lvl 15: Archetype feature
lvl16: ASI
Lvl17: Unspoken tactics: Ally within sight no longer need to talk to communicate, all have advantage against target of an AO when it is next to an ally.
lvl18: The right word: can replace any Persuasion, Deception or Intimidate roll with a 15, Int/day.
lvl19: ASI
lvl20: Tireless: Start every encounter with 1 momentum die.
Archetypes
Banner of the Healer: Remove more stuff with healing Pool, maximize healing items, ally can share HD on short rests, Camps are under a Sanctuary-like spell.
Banner of the Emissary: Expertise in cha-skills, create Calm Emotion-like effect, defeated enemies charmed, Insight Check to give enemy disadvantage in all social skill against you.
Banner of the Sentinel: avoid Surprised condition, ally can add Momentum to defenses, health-surge on critical, 1/2 damage when next to a 0 HP ally.
I think that would be an interesting class.