Been away a bit, but wanted to chime in. Here's a few 'themes' that are relevant to this signing:
The gamble - Of course it's a gamble. All contracts are. For the Eagles they already gambled on Wentz when they moved up in the draft and that paid off. No doubt Foles was the Superbowl MVP and the team couldn't have won without him, but I also don't think they win without the 11-2 record Wentz had as a starter that same season. Wentz, despite his injury history, has been worth it and it definitely worth an extension.
The cost - We have to remember it's all relative to the salary cap. Last season they spent 7.65% and 4.09% of the cap on the 2 QB spots being Foles ($13.6M) and Wentz ($7.3M). That's 11.74%, which isn't far from the three highest paid QBs being Wilson, Big Ben and Rodgers that hover between 13.9% and 14.1% of the total cap.
The Collected Bargaining Agreement (CBA) #1 - This isn't talked about much, but the CBA expires after the 2020 season. Just looking at the history there's a good chance players will want more money and will get some incremental increases above the slotted natural growth. In short the negotiated cap will continue to rise so teams have incentive to lock their 'franchise' guys up before that time.
CBA #2 - Currently the NFL includes total revenues into it's calculation of what the CBA is. That was
$14.2B in 2017 (couldn't quickly find something more recent). The one massive item that will be added to that mix is revenue from sports gambling. That increase is estimated to be an added
$2.3B in 2020. According to the second article that will be a 13.4% increase. That's net new revenue, so we can anticipate the salary cap to get one big bump when that's added and then when the NFL starts marketing it full bore it will grow faster. In short, the CBA can be huge.
The QB market - This market will get more dicey and have more unknowns. We have good young QBs like Goff, Dak, Mitch, Watson and Mahomes whom all have representation asking for top dollar. We'll also have some older QBs hitting FA (like Cousins) and there will be some players either retired or not worth a massive deal (thinking Brady, Brees, Ben or Rivers). I honestly think Dak will get an extension very similar to Wentz. After that the agents of Goff, Mitch and Watson now have the market price, so butting it off a year will only make that contract more expensive. In short expect your QB to cost around 15% of the salary cap and this number will continue to be a smaller % of the cap as the cap itself grows faster than the negotiated salary increases.
Why now? - 2 years ago Wentz looked like the MVP before the season ending injury. Last season where he was coming off a late season torn ACL, LCL and IT band which obviously impacted his ability to prepare for football. In that 'recovery' season he actually increased his completion percentage and passer rating from the MVP caliber season. Looking at this year he's been focused on football all offseason (the back didn't impact him at all) and he's got the best supporting cast he's ever had: Jackson, Jeffery (not missing the first 4 games with a shoulder like in 2018), Ertz, Goedert (who will be a monster), Agholor and a Mike Sanders/Jordan Howard running game and if he can stay healthy he might go full Mahomes this season. Things are lined up for a monster season so putting the extension talk out a year probably won't help lower what you are paying him.
In the end the Eagles know what they have in Wentz and the extension was more a formality. Even if he gets hurt again he's a part of their long term plans, so that doesn't change too much. From the Wentz side it's all about football and it will let him focus on executing without getting broken.