The slow emacs startup problem can be mitigated by lazily loading custom modes as much as possible. The two big things to use here are autoload (instead of require) and eval-after-load.
On my machine, a vanilla emacs startup is ~70ms, and one with my fully-loaded .emacs is ~240ms. Still not as fast as I would like, but not terrible. (You can benchmark emacs startup from the command line with "time emacs --eval '(save-buffers-kill-emacs)'").
(Of course, even a 70ms startup for vanilla emacs is arguably pretty bad -- it's way slower than the ideal of "instant"; I just checked and vanilla vim is something like 8ms, for example, which is just-shy of imperceptible.)
Using the Customize interface also helps. Variables that are customized go in a big list and don't get set individually, nor do they require their library to be loaded before they've been set.
A few years ago I went through my 10 years of accumulated .emacs cruft and switched everything I could to customize, and everything I couldn't to the technique you describe. I sped my emacs startup time from eight seconds down to one.
On top of that I switched to using emacsclient which makes startup instant.
Nice, I didn't know customize was faster. I'll have to try that.
emacsclient doesn't really work w/ my workflow -- when I want a new emacs, I really want a new emacs. Also worth noting you get something similar "for free" when using the gui emacs on MacOS, via open -a Emacs (I use an alias).
I wonder if you couldn't somehow snapshot the state of emacs and dump it for a truly fast startup?
On my machine, a vanilla emacs startup is ~70ms, and one with my fully-loaded .emacs is ~240ms. Still not as fast as I would like, but not terrible. (You can benchmark emacs startup from the command line with "time emacs --eval '(save-buffers-kill-emacs)'").
(Of course, even a 70ms startup for vanilla emacs is arguably pretty bad -- it's way slower than the ideal of "instant"; I just checked and vanilla vim is something like 8ms, for example, which is just-shy of imperceptible.)