To me that picture alone says this is a not a good idea.
To play devil's advocate would situations like that even happen? I doubt the defending team is going to try and hold the line in the same way if this was brought in. They'd be mindful that while the attacker is ahead of them, they can't be sure if he's ahead enough to be offside so the markers would all need to drop in.
More free kicks from a similar position on the pitch would be contested aerially with much fewer resulting in an offside. That could very much be seen as a good thing when it comes to free kicks.
I don't want it anyway, and at least some of it is because I'm used to what I'm used to and this would be a huge change.
We're also in a world where heading the ball is begininng to be seen as dangerous for long-term health. This would likely create more headers, as well as clashes of heads.
Detrimental, because it encourages kick-and-rush hoofball by giving a huge advantage to the attacker and disincentivizes high lines and offsides traps, meaning that many teams will just react by playing way deeper and more defensive than they do now. That might well overall result in slower games with less goals.
I can also see diving being encouraged, because attackers get a huge advantage over the defenders in free kick situations under Wenger's proposed nonsense.
I think that's how things would likely go too. Teams will stop playing for offside and offside traps are a 2-way street. Nobody thinks a team catching a player offside is exciting, although I suppose they can admire the coordination or how regimented a team is at stepping up in unison.
Offside traps fail too, and someone beating the trap can lead to big chances. If they're not looking to play offside, or least as nearly as much, then a particular type of chance from a long ball over the top or through-balls will be reduced in number.
There is a chance that with defences dropping deeper games could become more stretched and ultimately more end to end with players having more space to run into. In midfield areas in particular. Every game could be like United trying to defend counters under Ten Hag.
In some universe it could be more exciting but I don't know, could easily just be a slower game all round as you say and that would be my hunch too. Midfielders would have to learn to pace themseIves. Wouldn't like to see them take that gambleof bringing it in just in case it was detrimental to the spectacle.