This is just anti-overflow with an eraser, cf. Proposal: Anti-Spill/Anti-Overflow Option for the Brush Tool . It makes more sense to make a feature request and vote for an anti-overflow feature in general.
For developers/contributors: this anti-overflow feature exists in Drawpile, with the code available under an appropriate license, so it could conceivably be ported to Krita. Although it’s not too hard conceptually, each brush dab basically just does a magic wand selection constrained by the area of the dab and then the dab gets masked by that selection.