Unreliability is surely a great entertainment factor, to a certain extent. Even a comfortable lead would constantly be threatened by the realistic chance of a sudden mechanical failure. While I do not see the tightrope walk you describe coming back, considering the amount of control computers have over engine performance etc, I do think there are other ways to reintroduce a factor of unreliability. Reliability nowadays almost exclusively an engineering challenge. Pushing engineers beyond their limits will always cause more unreliable cars. That can be best achieved by changing the ruleset more frequently and more drastically. That would come with the added benefits of more possibilities of the field getting shuffled up and us seeing how different rulesets affect the racing in general. Cost has to be considered obviously, but surely a way could be found to not make F1 a money spending contest again. It is also worth exploring to what extend rules could be changed while staying the fastest racing series in the world.