On most models it's now down to about an $800 option. So the cost is minimal. And if it's done right it should be more reliable. Basically a redundant power system. Even if it only had 5-10 miles of EV range, in the event of a major engine failure, 5 or 10 miles could be a lot better than zero miles.

I haven't really heard of any one having issues with any manufacturer's hybrid system reliability. It's more complex. But I really have no reason to think it's any less reliable than the current drive train. Given that it will also reduce the stress on the engine by providing ev power at peak times - I think there's a pretty good chance that the system will last longer as a whole.

Even if the batteries need a replacement every 20 years - is that a problem? As long as the system notifies that it's needed and that a battery failure doesn't result in a broken down vehicle, I'm not sure I'd be opposed to that. I have to replace the normal battery every 4-5 years. If it saved me more money in fuel and maintenance than the battery replacement cost and gave me all of the benefits of EV drive - like unlimited fording depth, and probably great towing performance, etc. I'd probably be in favor of it.