I have to imagine framerates are going to be locked on online games but honestly if somebody is such a hardcore gamer that they complain about things like framerate or resolution giving other people an edge online and they are obviously paying for a high speed internet connection and a PS Plus/Xbox Live membership already.....I just can't see why they wouldn't be keeping up with the latest console.
I don't think devs will abandon the original either, hell if anything I'm sure Sony wants to sell more slims then anything. That is where the real money is made. Once you can get a console below the $199 mark you're golden. I think it will be a slow migration, games will just begin performing worse and worse on the original. If you played any cross platform titles on PS3 after the PS4 launched you will know what I mean. A lot of them were garbage towards the end. Which isn't necessarily a bad thing, it still gives people the opportunity to play the games but also gives them a kick in the ass to upgrade.