I don't think that would be good for WWE. Why give air and a write a huge angle for something you can't pay off?
They may as well get some mainstream attention out of it since they crave it so much as they head into the "dead" period of the Fall. They'll surely get those post-SS Raw viewers too which they can hook for the Fall with a big angle.
WWE so desperately wants to latch on to something and get some mainstream attention -- they did it with Rousey (who only now may have a match since she got destroyed in her last two MMA fights), they've tried doing it with McGregor who's routinely called them fake **** and called the entire roster *******. They just want the mainstream attention.
Jones sitting the front row and watching the main event wouldn't be so bad. Same way Undertaker was sent to a UFC show several years ago to try and goad Brock into an angle for Wrestlemania.
Let's face it -- there's a good chance Lesnar re-signs with WWE and gets paid the same 2-5M to do the minimum. WWE will probably be the ones allowing Lesnar to go do the fight. Last time they did so all they got out of it was promotion for their video game. I think they can get a little more this time in the way of mainstream attention with JJ attending and being shown on camera once.
I also don't think it would be good for the UFC either. It would come across as completely fake...
You'll get so much backlash from fans of the UFC that hate WWE.
1. It's fake
2. It's a rigged fight
3. Really? These two don't hate each other... they're just hyping a fight, everything they said is BS.
They're not even having any contact. Jon Jones would be front row in the crowd watching. He doesn't even need to leave his seat. It can be all Lesnar getting thrown off by his presence just enough to lose the title.
I did think of the downside, mainly from the UFC standpoint since WWE is scripted and all, but they're the ones who get the real fight. They're the ones who actually get Lesnar to do the fight (he could just not re-sign with WWE and do the fight anyways, but if Lesnar re-signs then WWE controls that).
Ultimately it won't happen, but I wouldn't mind seeing it and it'd be the most mainstream attention WWE would have in a long time which is what they're always after.