I don't see a rush to apply this patch. The bootimage writer historically has changed very slowly, so the risk of patch rot in the next month or two seems very low.
One should at least have empirical data for bootimage writing time with and without the patch applied for writing a prototype, development, and production image so that we can make an empirically guided decision.
I'm honestly less worried about slowing bootimage writing by a few percent than by the increase in stack depth causing problems for the host JVM and limiting our ability to build some configurations on some platforms. Can you quantify how much bigger the stacks need to be (run with different thread stack sizes for the host JVM with and without the patch and see where you start to get stack overflows).
3) is completely true, but also completely orthogonal to the question of whether or not this patch should be applied to the head or put in the research archive.
It's also not clear to me why this patch is worth prioritizing above the many other items sitting against 2.9.4 and 3.0.