Well, we don't hope that the new megas will replace the good old types.
In Germany, we can't say that the megas are cheaper then the old AVRs,
despite the fact that only few of the new types are really available.
Next point ist the package. Of course there are easy-to-use-DILs among
the newer types, but the more complex megas all come with fine pitch smd
packages, what makes prototyping or manunfacturing of small charges of
applications a lot more difficult. Personally, I will continue to use
2313 and 8515 al long as possible.