Yup. The fact that the recent UA didn't have alternate features to replace brutal critical was something I remarked on when taking the feedback survey.
It's the perfect place to add a few more interesting features
I like to 'brew, how about you? Design notes in italic.
Alternative Class Features - Barbarian
Brutal Weapon Master (Enhancement)
At 1st level, a Barbarian is considered to have the Great Weapon Master feat while raging, and may use its features on any strength-based melee attack, even if the weapon doesn't have the Heavy property.
GWM is pretty much a must-have for an effective Barbarian, and I don't like feat taxes. This also opens up some fun two-weapon barbarian builds that aren't gimped (!), as well as gnome barbarians (!).
Reckless Critical (Alternative to Brutal Critical 11 13 and 17)
While Raging and making a Reckless Attack, you score a critical hit on a 19-20. When you strike a critial hit while Raging and making a Reckless Attack, you deal 1 extra die of weapon damage, and gain half of the damage you deal as temporary HP until the end of your next turn.
This increases to 3 dice at level 13 and 6 dice at level 17.
Dipping Hexblade 1/Fighter 3 for 19-20 criticals is a very common trope for barbarians so I just rolled it in here; with perma-advantage they really want to up your critical rate, as the ROI is doubled. This costs you non-reckless non-rage criticals at the benefit of them being 2x as often when being reckless and raging. I then up the dice you gain at 13 and 17 so those levels don't suck (2 dice instead of 1).
Inner Rage (Improvement to Persistent Rage)
You always have advantage on Strength, Charisma(Intimidation) checks, Strength saves and saves against being Charmed or Frightened.
Might as well give the Barbarian some (I mean, a) social (I mean "social") skills (I mean, skill). And "I rage to do a str check" now goes away, giving the barbarian more things to do in exploration. The 3 saves are things I could imagine having a reserve of Rage would help against.
Indomidable (Improvement to Indomidable Might)
When you roll a d20 for a Strength check or save, Constitution check or save, Wisdom save or Charisma(Intimidation) check or Charisma save, if the roll is under the statistic in question, you instead are considered to have rolled the statistic value.
So if you have 12 Charisma and +7 intimidation, the minimum intimidation roll you can get is 12+7=19.
This is a level 17 ability. It is a bit redundant with the new Inner Rage. But it shores up mostly strong points of a Barbarian, plus the boost on all Wisdom saves.
A 24 stat barbarian with proficiency has a min (and hence max) roll of 24 + 6 + 7 = 37 on a check/save. Yes, this means it may be impossible to break a barbarian's grapple. Deal.
Overall: offensively, this gives the Barbarian a bit of the Paladin crit-fishing; they do 7[W] on a crit. Less than a Paladin full smite, but comparably scary. Whirling Scimitar barbarians become interesting with 3 attacks at -5/+10.
It also gives them a few toys in the exploration realm and social realm in the back half.
And it shores up one or two defensive weaknesses, and some already existing strengths, in I hope a fun manner. A 14 charisma/wisdom/con/str barbarian with resilient (or other proficiency) has a min save of 22, for example, or 16 without the proficiency, and often have advantage on the save.