Is there a good reason this isn't already patched to allow sending 0 in power kernel and cssu kernel? I.e. is there something horribly_dangerous™ about sending 0 to that watchdog? I'll probably go ask the current power kernel maintainer to do it eventually, if there isn't, just because less user choice ultimately = worse.

Fair enough: I'll look into this in detail a little while later, and see if I can adapt said checks from your watchdogs binary source into my preinit mod, but personally at the moment I find installing bootmenu or manually fetching the binar to be less convenient than using busybox-power (since I already always install that), for my purposes, even knowing this issue you've pointed out, and I imagine this is true for some other people as well.