Any chance on a port to D7?

Yes, have a go! It's a pretty simple module and the menu functions look like they haven't changed that much
menu_block_split uses the following menu functions

D6 -> D7
menu_set_active_menu_name -> menu_set_active_menu_names
menu_get_item -> menu_get_item
menu_get_menus -> menu_get_menus
menu_navigation_links -> menu_navigation_links
menu_load -> menu_load
menu_tree_page_data -> menu_tree_page_data
menu_get_active_menu_name -> menu_get_active_menu_names
menu_get_active_trail -> menu_get_active_trail

Have a good look at these functions at api.drupal.org to make sure there aren't any changes in the parameters and output.

hook_perm() is now called hook_permission() and has a different structure

hook_menu() will need a path change from 'admin/settings/menu_block_split' to 'admin/config/user-interface/menu_block_split'

hook_block() has also been changed, now uses several functions. This is probably the hardest part.

hook_theme() has been changed but it's pretty straightforward and the theme functions will need the parameters changed, now all in one array.

There is one db_query() that will need to be edited

The rest, with any luck will need very little change.

see http://drupal.org/update/modules/6/7

subscribe

There's a release, right?

7.x-2.x-dev is available and I have just commited some very minor improvements, eg CHANGELOG and a hook_enable() to remind users to configure.