I'm not sure how it makes things harder for the PL. If a deal is above FMV they can reject it. I really fail to see any meaningful advantage to clubs knowing what others are getting in relation to FMV. What is FMV for Newcastle shouldn't be a surprise to Newcastle. They don't need to be told what Villa are getting to know what, give or take, they can legitimately put through as FMV.
Ultimately what Newcastle (or whoever) can successfully argue is FMV is the same value that they should be able to secure on the open market so I don't really care if Newcastle sign a deal with Saudi Telecom for £10m instead of EE. You can argue it makes Newcastle's work easier but ultimately you're not going to benefit for greater commercial deals through this change.