4th-level and higher feature (enhances Ability Score Improvement)
Whenever you gain the Ability Score Improvement feature from your class, you can also replace one of your skill proficiencies with a skill proficiency offered by your class at 1st level (the proficiency you replace needn’t be from the class). This change represents one of your skills atrophying as you focus on a different skill.
Commentary. I like this; it's a pretty basic "re-training" option. This is probably a good one to adopt for longer-running campaigns; by fourth level you might have figured out that someone else in the party is better at Investigation than you are, so swap that skill out for something you'll get to roll more often. I bet if this makes it to publication they will change the wording from "needn't."
2nd-level barbarian feature (replaces Danger Sense)
You become proficient in your choice of two of the following skills: Animal Handling, Medicine, Nature, Perception, or Survival. Your proficiency bonus is doubled for any ability check you make that uses either of those skills.
Commentary. This is an interesting replacement option because it isn't strictly better than the feature it replaces, which means it's a real option instead of a patch. Danger Sense's advantage on Dexterity saving throws is pretty good, but this is a nice way to squeeze in some non-combat utility into the barbarian class.
5th-level barbarian feature (replaces Fast Movement)
When a creature ends its turn within 15 feet of you, you can use your reaction to move up to half your speed to a space closer to the creature. This movement doesn’t provoke opportunity attacks.
Commentary. This is another replacement option that doesn't obviously overshadow the feature it replaces. If anything, this one strikes me as being fairly situational; if your group uses a grid map for combat, Instinctive Pounce probably has more value than if you don't.
1st-level bard feature (enhances Bardic Inspiration)
If a creature has a Bardic Inspiration die from you and casts a spell, the creature can roll that die and add the number rolled to one damage or healing roll of the spell. The Bardic Inspiration die is then lost.
Commentary. I don't really get why this would buff spell damage but not weapon damage. I guess this offers something extra to casters who rely on saving throw spells vs. attack roll spells.
1st-level bard feature (enhances Spellcasting)
Whenever you finish a long rest, you can replace one spell you learned from this Spellcasting feature with another spell from the bard spell list. The new spell must be the same level as the spell you replace.
Commentary. Note that this feature is also available to rangers, sorcerers, and warlocks. This is a great enhancement for classes that feel a little starved for choice when it comes to spell selection, particularly the sorcerer. One thing I would like to see added here: also make this feature available to Eldritch Knight fighters and Arcane Trickster rogues!
1st-level cleric feature (enhances Spellcasting)
Whenever you gain a level in this class, you can replace one cantrip you learned from this Spellcasting feature with another cantrip from the cleric spell list.
Commentary. Note that this feature is also available to druids and wizards. Much like Spell Versatility, this is a good way to get a character out of a bad choice. Part of me wonders if this feature exists to let people off the hook for taking the True Strike cantrip.
Channel Divinity: Harness Divine Power
2nd-level cleric feature (enhances Channel Divinity)
Note that this feature is also available for paladins. You can expend a use of your Channel Divinity to fuel your spells. As a bonus action, you touch your holy symbol, utter a prayer, and regain one expended 1st-level spell slot.
Commentary. I'm not that familiar with all of the Channel Divinity options, but this features feels like an option that exists to patch some duff ones. Gaining back a 1st-level spell slot doesn't feel that powerful, so I wonder how useful Harness Divine Power really is.
8th-level cleric Divine Domain feature (replaces Divine Strike or Potent Spellcasting)
In battle, you are blessed with divine might. When a creature takes damage from one of your spells or weapon attacks, you can also deal 1d8 radiant damage to that creature. Once you deal this damage, you can’t use this feature again until the start of your next turn.
Commentary. This is a decent replacement for Cleric domains that give you Potent Spellcasting, since it applies to both cantrips and all other spells. But it's not a good swap for Divine Strike since it doesn't scale, unless you want the versatility of a bonus on both weapon attacks and spells.
2nd-level druid feature (enhances Wild Shape)
You gain the ability to summon a spirit that assumes an animal form: as an action, you can expend a use of your Wild Shape feature to cast the find familiar spell, without material components.
When you cast the spell in this way, the familiar is a fey instead of a beast, and the familiar disappears after a number of hours equal to half your druid level.
Commentary. This enhancement feels very situational, as just about anything a familiar could get done for you is something you can do for yourself while in wild shape. It can, however, provide a source of Help actions during combat. Still, it has good flavor and doesn't seem to break anything. (Also, does it take an hour to summon as per find familiar?) I wonder if it would be more satisfying to have a "pet subclass" for the druid instead.