One major feature that Krita is missing, which makes rendering objects to look less like polished plastic much easier, is the ability to modify each brush dab/stroke with a mask made out of another brush. It seems like the development of this has been going on for around a year or so, but are we ever going to see any updates on this?

We're working on it https://phabricator.kde.org/diffusion/K ... ked-brush/

The issue has been one of lack of manpower, which was primarily sucked away by the qt5 port.

It's been more than two months, and aside from that one commit on September 27, it seems like no further work was done on this feature. Has it been abandoned?

No.