Give the engineers a little bit of credit for being able to mitigate a problem when their attention is focused on it.
I have issues with that statement at many levels:
First, are these the same engineers who designed the Lithium-Ion battery system (and oversaw the whole design/implementation/testing process) in the first place?
Two, definition of mitigate is to "Make less severe". Any fire (other than the engines), is a no-no on any aircraft, period. I'm not interested in a fire being made less severe, I am however very interested in not having it happen in the first place.
Three, if building an incinerator box for the batteries, albeit a vented one is what these engineers come up with when their attention is focused, I for one am not impressed.
IMO, this is a patch, it's the quickest means possible of getting the planes flying again - beancounter engineering.