Converted to configuration:

config_sync_batch_size => system.core (50)
default_nodes_main => system.core (10)
filter_fallback_format => system.core ("plain_text")
user_cancel_method => system.core ("user_cancel_block")
private_key => system.core private_key (0)
file_temporary_path => system.core file_temporary_path ('')
file_public_path => system.core file_public_path ('files')
file_private_path => system.core file_private_path ('')
install_profile => system.core install_profile ('standard')
clean_url => system.core clean_url (FALSE)
file_default_scheme => system.core ('public')
image_toolkit => system.core ('gd')
theme_default => system.core ('stark')
admin_theme => system.core ('')
node_admin_theme => system.core ('')

Converted to state:

javascript_parsed
test_module_enable_order
test_module_disable_order
js_version_query_string
block_test_caching
node_access_needs_rebuild
config_sync
menu_rebuild_needed
menu_masks
update_last_check
update_last_email_notification
install_profile_modules
path_alias_whitelist

Converted to settings:

css_gzip_compression
js_gzip_compression
mail_line_endings
queue_class_*
queue_default_class
queue_default_reliable_class
404_fast_paths_exclude
404_fast_paths
404_fast_html
mail_system
password_count_log2
password_inc
session_inc
lock_inc
cache_backends
page_cache_without_database
page_cache_invoke_hooks
allow_insecure_uploads
filter_allowed_protocols
session_write_interval
stale_file_threshold
file_chmod_directory
file_chmod_file
maximum_replication_lag

Deleted:

weight_select_max
menu_override_parent_selector (https://www.drupal.org/node/191360)
file_description_type
file_description_length
file_icon_directory
image_style_preview_image
menu_default_node_menu (only used within Views module)

Introduced in branch: 
1.0.x
Introduced in version: 
1.0.0
Impacts: 
Module developers
Theme developers
Related Github Issues: 
https://github.com/backdrop/backdrop-issues/issues/170