Honestly I don't really like the idea of ward kill experience. It's very dependant on you being good at finding wards and killing them and that also depends on the other team placing them, not to mention the support scanning the right areas. For lower elo especially this wouldn't help supports as much.
I also think it's very unintuitive to players who don't know know every hidden mechanic, like new players especially. And it does have the potential for weird interactions with other roles, etc.
Why not just add an experience rubberbanding effect to the bandit mastery or support items, like if you're the lowest level on your team you gain bonus exp, until you're caught up to the next lowest, usually the adc? I can't see mid laners abusing that since they're generally the highest level player
Edit: and what if the correct play is to scan a specific brush you need to not have vision in, compared to knowing they placed a ward somewhere not that useful, them you have a choice between the wrong play to get exp and the right one. There's a lot I don't like about it