iFrames are definitely here to stay - for the time being anyway! Although they are not as readily available for the 'non-coder' Fan Page owner to access like fbml code was, iFrames certainly offers a lot more than fbml could ever do - and hence the reason Facebook switched.
Tag: FBML code
No More FBML for Creating Custom Fanpages
No need to panic though! Facebook will still support Fanpages already using FBML code. It will only affect Fanpages wanting to create a custom page from 2011. Here's an excerpt from Facebook Developers list of changes expected in the first quarter for 2011