For MicroB, the engine is open, the UI is closed.

I don't really know why WebKit is in any way better than Mozilla's engine, but that's just my uninformed off the top of my head thought.

No one's working on a recode of the MicroB UI as far as I know - which would be the easiest way I would think towards upgrading the engine - since the UI being closed source probably means you can't just plop in a completely different engine like WebKit (an upgraded Mozilla Firefox engine might be doable, though honestly, I don't know how it needs to be compiled, so someone more knowledgeable can probably state more accurately what could actually be done. MohammadAG briefly worked on a QT web browser that looked very similar to MicroB iirc, but last I asked him he stopped doing anything with it a while ago.