I'm referring to this issue #30746 that was closed with limit of 125MB staying fixed opposed to being configurable.

It was argued that there would be no common cases hitting the 125MB limit. Such cases probably never occur on UI but there are such cases...for example if you have a REST API that returns JSON document which has some document encoded as a base64 in a single field or it has another JSON document nested inside a single field as a string which is used for digital signing and verification of it.
And i have such a case where i'm digitally signing some JSON document and the creating a new JSON where the payload field (contains my JSON document) is larger than the 125MB limit.