The two-under concept might also be applied to Precision/Neapolitan 2C openings and the defense thereto, or to 3C openings.
Double = one or both majors, competitive only. Partner bids 2/3D (cheapest) with spade preference.
2/3D = majors, extras
2/3M = intermediate overcall.
This is the rough sketch structure. Tweaks might include that the cheapest diamond call is Michaels-style and the double takeout-or-major. The idea would be to solve a problem with a 2C opening, namely that 2M might make sense with a weak two hand up to an intermediate with six-bagger. Forfeiting diamond overcalls and diamond responses to the double vastly improves major sequences.
Just a thought...