I think the new system of cost-progression really adresses the issue of gold-inflation effectively (and by that yield-inflation in general, since all yield-producing buildings are purchasable via gild).
What I was thinking about was, if that system should also extend to the building of wonders. Right now, after having already built up a huge city one can encounter the strange situation that building a wonder costs considerably less production than ordinary buildings. It feels counter-intuitive when a unique wonder requires less effort to build than a staple building.
Not only that, I think the gameplay-experience could profit as well, since introducing a cost-progression also for wonders would allow players / the AI to catch up. Eg.: Someone lagging behind can have a shot at building wonders, if the wonder in question would be the first for his/her city, whereas the one to compete against would face much higher production costs, if for him/her the wonder would be the 4th, 5th or even 6th. This would also make you think more strategically about which wonders to build, and you'd likely be less inclined to just build any wonder for adjacencies sake, if the specific boni don't interest you.