Tasker can certainly change settings and launch apps, so I don't see why Cortana couldn't. Maybe Microsoft just means it's more difficult? They do say certain features "won't initially be available", which implies they will in the future, though this contradicts the statement that the features "won't work".

Hands-free voice control is tricky because Qualcomm controls hardware support. There are some workarounds if you don't want to license Qualcomm's tech, but I guess Microsoft may not want to use such hacks. Otherwise, without Qualcomm's dedicated always-on voice coprocessor, leaving the mic on would drain the battery.