There has always been a "work around" for doing this kind of development. It involved still having an .ascx but with nothing in the HTML code and all implemented in the code behind instead. I've done a number of modules this way.
New to 4.5.0 is the ability to completely create server controls with no .ascx at all. Unfortunately, I don't think it is "complete" yet.
Go to Charles Nurse' blog and look for his "Look Mom, no hands" article. It gives an example in "Hello World" fashion. Problem is, that it is only the "View" part and has no other examples.
Charles has said he'd look into it a little further and get back to me. I'll keep you posted.
My module I am creating is a Weather module (currently using the Yahoo Weather Rss service) and I was easily able to get it's "View" part working and rendering perfectly. What I couldn't get working was:
1.) Nothing other than View definitions worked.
2.) Couldn't get AJAX working.
3.) Couldn't get localization to work.
Of course, I'll keep on trying...
;)