At the farthest reaches of powerful software, you will always end up with a programming language and libraries.
At the other extreme, you have one thing that does exactly one task and as such can have a nearly "invisible" interface.
My suspicion is that it's actually kind of rare to need the areas in between - that apps like spreadsheets and photo editing are unusual, and if you _suspect_ that you have an app that could be developed in such a broad, deep, configurable way, your best bet is to start building in a library form and construct prototype one-shots - possibly even making them your MVP - attacking various different problems to see if you're right, before you try to make a unified monster UI for the perceived need.
At the other extreme, you have one thing that does exactly one task and as such can have a nearly "invisible" interface.
My suspicion is that it's actually kind of rare to need the areas in between - that apps like spreadsheets and photo editing are unusual, and if you _suspect_ that you have an app that could be developed in such a broad, deep, configurable way, your best bet is to start building in a library form and construct prototype one-shots - possibly even making them your MVP - attacking various different problems to see if you're right, before you try to make a unified monster UI for the perceived need.