Its a big thing to ask, however i'll try anyway.

We are splitting up our main app and it is easy to end up with a lot of tiny extensions to cover for cross extension functionality. Sort of bridge functionality between our main extensions. So I thought why is it not possible to have a depandancy marked as optional? So we are always developing / compiling with all dependancies, however when deploying for all optional extensions the following should happen:

1. page and table extensions to a non existing optional dependancy should not result in error, just be ignored
2. subscribers that subscribe to a non existing optional dependancy should not result in error, just be ignored.
3. fields that have tablerelations to a non existing optional dependancy should be ignored (or tablerelation removed) or should not be allowed
4. page actions that reference a non existing optional dependancy should be removed
5. codeunits that implements an interface of a non existing optional depencancy should ignore the interface
6. functions with variables that reference objects in a non existing optional depandancy should not be executed, however can be savely called from within the app. Function should do nothing.
7. probably I will be overlooking 2 or 3 things I realize that :)

"dependencies": [
{
"id": "My App ID",
"name": "My App",
"publisher": "My Company",
"version": "0.1.0.0",
"optional" : true
},

>> subscriber function to a publisher in an optional extension should be ignored
[EventSubscriber(ObjectType::Table, 1234, 'OnDiscoverSubscribers', '', false, false)]
local procedure OnDiscoverSubscribers(var IAmAnTableInAnOptionalExtension: Record OptionalExtensionTable)
begin
OptionalExtensionTable.AddSubscriber("ItsMe!", '');
end;

>> every function that has a variable to an object in an optional extension should compile, however code inside is not executed.
local procedure LogError(ErrorText : Text)
var
IAmAnTableInAnOptionalExtension: Record OptionalExtensionTable;
begin
IAmAnTableInAnOptionalExtension.LogError(ErrorText);
end;