Busty Box 1 is 1st person for most of the fights, with various animations in 3rd person, from grabs to special moves. Busty 2 is entirely in 3rd person except for the Sam's Fight spinoff along with the training minigame plus the ninja minigame, those are in 1st person.
Modding flash games is simple enough once you understand either converting the file with Flasm to a document to change numbers for hp or even enemy behavior or use FFDec to decompile the swf file and directly alter the graphics and sound. I'd say the issue is more likely to be that creating an entire new engine is likely easier due to discontinuation of Flash Player's support. That and even if such a game is made, the only ways to really play SWF files now are either through the Standalone Flash Player, Newground's Flash Player, or a few others I can think of, along with Webgenie or Flashfox for android
Barbarianbabe's games seem to mostly have series of images for animation, and sounds for sounds, which can easily be reused in another engine, such as Game Maker or something else 2d. Hell, even RPG Maker could actually pull it off, though that would be far too much effort for the results. As long as it can play a series of images with sound, the system can be anything.
Aside from all that, another game I'd like to see a sequel to would be Galaxia 2.