Ability Scores themselves don't get used much in modern D&D, compared to their associated modifiers. However, it occurs to me that the Ability Scores themselves correspond nicely with the normal range of Difficulty Class target scores.

For example, an Intimidation check can use the target's CHA score as the DC. Likewise, Persuasion and Deception could be compared to the target's WIS and INT respectively. You could also add the target's PB to the DC if they had proficiency in the same skill, representing the idea that it's harder to Intimidate someone that knows the tricks and techniques.

For these social skill checks, I prefer this method to a contested check. If the target is required to roll the dice, it feels like they are aware of being Intimidated and actively trying to resist it. However the reality in-game is generally more spontaneous, so I'd prefer a static target, much like a Stealth check is compared to the passive Perception of an unwary target. 

Has anyone employed anything like this before? Can you suggest any problems with this? Any improvements?

So how do use this for DC 20, 25 and 30 target checks?

Like, the Noble has 14 Wis and 16 Cha. So by your rules convincing him to sell his title to you is just going to be a 14 or 16 DC, when realistically it should be more like 25, at least. How would your rule account for this?

Quote from ZorgAlmighty >>

Ability Scores themselves don't get used much in modern D&D, compared to their associated modifiers. However, it occurs to me that the Ability Scores themselves correspond nicely with the normal range of Difficulty Class target scores.

For example, an Intimidation check can use the target's CHA score as the DC. Likewise, Persuasion and Deception could be compared to the target's WIS and INT respectively. You could also add the target's PB to the DC if they had proficiency in the same skill, representing the idea that it's harder to Intimidate someone that knows the tricks and techniques.

For these social skill checks, I prefer this method to a contested check. If the target is required to roll the dice, it feels like they are aware of being Intimidated and actively trying to resist it. However the reality in-game is generally more spontaneous, so I'd prefer a static target, much like a Stealth check is compared to the passive Perception of an unwary target. 

Has anyone employed anything like this before? Can you suggest any problems with this? Any improvements?

 
That’s what passive scores are for. Those would typically be the DCs for thos kinda of things. Just use passive Wisdom/Charisma (Insight) as the DC for those Charisma (Intimidation) checks. Stuff like that.