To begin with, there are no real changes. The only changes are that server owners no longer can sell ranks in their server. The reason why was many kids had spend hundreds of dollars on ranks and asked for a money refund, but server owners refused. I know that money goes to the server to keep it up, but many servers have so much money that, the server owners can spend the spare money on real life things. Although not all servers are converted to 1.8, many buycraft donator shops have a half price on each rank.
90% of servers have a lot of money and can last up to 3-6 years long! Owners can get sponsors or make youtube videos to earn money. Mohjang still allows owners to sell perks such as, Pets, Name Tags and etc. Mohjang wants all players to have a fair gameplay.
I wish to state more facts, but this is a opening statement! Your turn!
To start off, it seems Mojang has been quite lenient when making exceptions to the rules, so it still appears unclear what the terms are. First off, taking away gameplay advantages that some players had will even things up between those with money to spend on the game and those who don't.
However, the big change will be in how server owners will attempt to make up the deficit from the funds that they might not be receiving. Notch specifically allowed an exception for owners who want to make their servers pay-to-play to charge customers to be white-listed. This will still cause problems for those that do not have the money or the time to pay to join a server. I will get into how this could affect the game further in my next point.
Their is really no change of gameplay because donator will keep their ranks and items, it just that starting from 1.8, people can't buy donator ranks anymore. Majority of server owners have a lot of money to last 3-5 years. Whenever I see a donator pvp just outside spawn, they are the people that destroy kid's gameplay. They are getting donator kits that are far more better than regular kits you get when you first join the server. It takes a lot of time to get good armour and swords as a regular player.
I wouldn't say there will be a direct change in gameplay, but over time, more servers will close or become pay-to-play. But the difference on PVP, factions, and related servers will be that there will be less OP items in circulation and there will be more balance. Keep in mind that a relatively positive change is still a change. The biggest shifts will, however, happen in the administrative part of servers. Another think that might change is whether the developers of major plugins will stop developing due to decreased donations.