"There's probably not enough space for a meaningful exploit" is never a strategy that pans out. Hardcoded signature validation can go a long way, but of course

"There's probably not enough space for a meaningful exploit" is never a strategy that pans out. Hardcoded signature validation can go a long way, but of course it really needs to be bulletproof, and also take e.g. downgrade protection into consideration. An added physical switch, while more secure, is (as the previous commenter mentioned) so impractical, that it will more likely lead to less updating of vulnerable microcode.