They only are releasing this to steal some thunder and some press from the Bronco.
Jeep revealed the 392 Wrangler the day before the Bronco reveal, so in order to have a running concept, that is pretty much ready for production, they would have to have been working on it for years already. It's likely the JL platform was already designed with the HEMI in mind. Remember, this is a new platform that has only been out for 2 model years.
The Bronco is going to tear the wrangler up in sales next year I am afraid.
Doubtful. The Wrangler created the niche it's in. The Bronco will have a fierce battle to over through the king of the hill. There are so many factors that come into play here, but I think the big one is the numbers we've already seen. The Wrangler sold around 230,000 units last year. The Bronco on the other hand only got 150,000 reservations. We all know reservations aren't sales. An optimistic guess would be that 70-75% of those reservations will be actual sales, but the truth is its more likely to be 60-65%. So expect actual first year sales of the Bronco to realistically be more like 100,000 Units. But, probably about 80% of Bronco buyers wouldn't even consider a Jeep for a number of different reasons, so that means the Wrangler will likely only loose about 20,000 sales. While Jeep wouldn't be thrilled with that they still sell around 210,000. Not exactly a kill it off year. After the hype of the Bronco cools off it will likely do even less damage to Wrangler sales in the second year.
Then there's the real kicker. The MSRP on the Bronco is comparable by trim level to the Wrangler. However, we all know that dealers will be marking them up the first year. Meanwhile Jeep will be 3 model years in with the current Wrangler, meaning they'll already have a return on their investment, so they'll be able to afford to offer discounts on Wranglers, The combination of these 2 factors will make the Bronco significantly more expensive than the Wrangler, and likely secure sales with buyers who have been dreaming about a Wrangler for awhile.