I'll just add in here what I tend to always parrot in these kinds of hypotheticals; this is why I no longer play in leagues where you don't pay for trading future year draft picks. I understand there are collusion scenarios that this safety net wouldn't catch (like some collusion-style player for player with promise of swaps/exchanges in the future, etc.); but it does discourage some forms of collusion, as well as just generally forcing owners to care about the league integrity along with their own team in the current year they are playing. Makes people think twice before mortgaging the future when they are paying for that future up front and can't just dine and dash.
Yeah, all my dynasty formats are like that. Wanna deal your 1st & 2nd rounders for the next 2 years? Go for it, but you’re paying for those years immediately after the deal is consummated, so if you bounce, the next owner gets a however many free years.
IMO it’s the only way to do it.