Opening multiple files in a single buffer?

[Gregory Heytings]

Dear List,

I've now been using Emacs for many, many years, and there is perhaps a 
single feature I'm really missing, namely opening more than one file in a 
single buffer, with the contents of the files appearing one after the 
other in the same buffer, with some kind of visual separator between them. 
I don't know if that feature exists in other text editors.

For example, suppose you write a book, which has fifteen chapters in files 
chap1.tex, ..., chap15.tex.  Opening these files in a single buffer means 
that you could use isearch-{forward,backward} in the whole book.  (I know 
that multi-isearch-buffers could be used in this particular case, but it 
is not as convenient to use.)  You could also use query-replace on the 
whole book, or reindent all files, or execute shell-command on all files 
at once, and so forth.  (Again I know that all this can be done with 
already existing features, e.g. through dired, but again I find them not 
as convenient as what I have in mind.)

Each file would have its own major and minor modes, and the mode-line 
would adapt depending on the file corresponding to the buffer portion in 
which the point is currently located.

My question is: Is this feasible, or is the one-to-one correspondence 
between buffers and files too deeply rooted in Emacs' codebase that it is 
not feasible?  If it is feasible, could this feature be considered for 
implementation in a future Emacs version?

Gregory