It is actually not straightforward to switch the code. In general, you cannot really just swap out a GUI toolkit, that influences the design of the entire program. If there are good security focused libraries that work here, and there is a reasonable upgrade path for them, then I would expect GNOME to also start migrating towards that too.

I personally wouldn't bet on their desktop, in the past few weeks their developers have made a number technical statements that seem very bizarre and confusing to me, and have openly said they don't really have the manpower to keep up with GNOME.