Dear Nick,
You can do a workaround to know what ids were consumed:
Use the below URL's to know:
My server instance is BC140 if your is different then change it accordingly, or if you are using an online version then replace "">">">http://localhost:8080/BC140/" with your Business Central Online URL:
To see all the base or custom used objects by directly accessing the table or page:
For Page: localhost:8080/.../
For Table: localhost:8080/.../

To check all the used objects in an extension follow the below steps:
1: Identify App Package ID:

2: Open this URL: localhost:8080/.../ filter based on App Package ID by doing this you will find all the objects information that you used in the extension

http:// localhost:8080/BC140/?page=9174&filter=AllObjWithCaption.'Object ID' IS '50000'

http:// localhost:8080/BC140/?page=9174&filter=AllObjWithCaption.'App Package ID' IS '070f0b31-1e63-4774-a251-1214ea3c7ee1'

Another Workaround you can use:
You can also Explore AZ AL Dev Toolz/AL Code Outline to see Object ID's in different App Package ID:

Microsoft_Application BC14 Objects:

My Custom Solution App Objects:

I know this is not the exact solution, but using this workaround at least you will have an idea to know what objects id are consumed if you just copy the filtered records in excel and sort by Object ID this will be very helpful.
As you asked a very good question, very soon I will try to find a better solution for sure to identify all the used object ID and will share it with you.