" pull out an Elgg core version without the view system" YES! & that sounded like what you wanted  /needed for yr Apps/Layers 'nodes' - if u r demaracating via node|function - the 'split' would have been inevitable. start.php may be fine.. but you'll also find script files (trbl spots?;) where e.g. elgg_list  and elgg_get functions are mixed - the _list_ will invoke *views which u do not need.. --> 'split code files' ?? u might be looking at some sort of re-structuring of elgg along the way ;-) if you do - i am cofident that a fair bit if what you encounter and resolve will end uo being useful for elgg design in general.what u r doing kinda vaguely resembles my 'distributed elgg directions - presented @elgg hootenany some years ago @Boston) - same sentiments..

You can safely remove the following libraries too,

• calendar, 
• export, 
• opendd, 
• and if you are sure that you are not using any deprecated functions in your plugins, just remove those two massive deprecated libraries too.

In our install, we have removed the above libraries with web_services too. 

@Team Webgalli  good tips, thanks!

@DhrupDeScoop  thanks for feedback