Something I'd dearly love to see in negotiations is the ability to explain *why* you're walking away from discussions. Say my player comes to me demanding a new contract and say I'm bonkers enough to agree, but right from the start his agent is insisting on there being a minimum-fee release clause that's far too low.
Now, I'm not about to risk losing a key player for such a low fee but I also don't want to break my promise to the player that I'd offer a new contract. Of course, I can just walk away and say "I promised to make an offer, it's not my fault you didn't accept it" but frankly that's a bit too confrontational, and the "I'm genuinely sorry, I promise to try again" is too far the other way.
What I'd like to be able to do is have a drop down list or a pop up box when you hit "Walk away" that lets you pick some options: wage demands far too high, agent demanding a release clause, agent not being flexible over demands, etc. I get that with the number of reasons one might walk away from negotiations that this could be quite an ask, but it could probably be reasonably summed up into half a dozen options.
Additionally, when you walk away and then go back to speak to the player it would really help if there were another dialogue choice that isn't either a grovelling apology or telling them to jog on - "Look, I entered into negotiations with you/your agent in good faith but unfortunately we just couldn't come to an agreement. I'm prepared to restart talks if you/your agent can agree to be a bit more flexible."
(Actually, that last point applies to a lot of player interactions when you've "broken" a promise - you can either grovel and beg for forgiveness or tell them to get stuffed; there's not a middle-ground compromise option.)