Okay, that makes sense, we just have different opinions on that feature which is fine. Especially since we all have our different opinions about balance, and each group balances differently due to house rules.

If I were to made the changes my way, I would've made the DC change to str like you did, and left it as is. My reasoning, is that I felt the frighten condition was thematic, but was it strong, yes, but you have to give up your action to do so. Intimidating Presence doesn't specify that you must be raging to use it, which adds a more versatility to the barbarian since it doesn't have that restriction. Even while you are raging, yes, like you stated to be for sure that you can maintain it you must go into a frenzy to use your bonus action attack. I feel like this was a good trade off, because it gives more of a reason to use frenzy rather than just to have another attack.

It also acts as a different form of taunt for the barbarian because the way you currently have it; I feel that with yours as an aura that impose disadvantage steps on toes of the ancestral guardian a bit too much. As an aura you are imposing more disadvantages, than the conventional taunt tank subclass. The ancestral guardian can also only target one creature with its mark, but the difference is that there's puts disadvantage to everyone else, while the Intimidating Presence give the creature disadvantage for you, so I can agree with it being a bit stronger because of it being more creatures are disadvantage vs 1. Then with attacks, because Intimidating Presence uses your action and have to use frenzy to attack on the same turn, your only maybe getting 1 attack, while the ancestral guardian still gets their two attacks. So overall I feel it they balance each other out without stepping too far one way or another.

But just like you, I haven't been able to test this out either, nor have I played the berserker due to its short comings.

Thanks for the comment! 

The problems I had with the original ability (Intimidating Presence) is that it only impacts one creature at a time while also taking an action which technically would end a rage since they would not be attacking someone during their turn. You would have to use the ability while not raging or in a frenzy which makes it kind of an odd duck. By making Intimidating Frenzy an aura while in a frenzy it ties it more strongly to the key ability of the class. We also don't want it to take an action, bonus action or reaction as it would get in the way of other abilities of the class. If I had left it bestowing the frightened condition it would have been too powerful so I toned it down to just giving disadvantage. 

I am up for suggestions if you think of an alternate. Or if you play it a bit and have some experience to share. Unfortunately I have not had the opportunity to playtest just yet. 

Overall I do like the changes that you made, because they do fix a lot of the issues of the beserker subclass. Though I think that the Intimidating Frenzy, would have been good the old way if it was just had been changes to str instead of cha. Just curious on why you changed it to an aura that imposes disadvantage on attack rolls instead.

Seems really powerful.