Hello That is also good idea but few drawbacks:
This component is very old and impossible to find.
Also is this reliable enough?
Will the failsafe detect correctly when to activate itself? What happens where there is no PPM at all or PPM with wrong pulses coming into this decoder? after that how will the decoder affect the PWM output for the servo channel so that the failsafe can detect this and activate?
Also what is the resolution of that decoder? Is it 10 bit?
And last but not least: whats the difference between CD 4017 and CD4020? I read the datasheed and it comes out that 4017 is 10 channel and 4020 is 8 channel.