More flexibility on TMS xyz tiles syntax
As it has been pointed out in this Idea, ArcGIS Online allows to call in TMS xyz tiles from external providers. I will not focus here on the question to have an equivalent option in Pro as it is already being discussed there, but on the way they are imported in AGOL.
However, importing these tiles often requires tweaking of the xyz parameters, which the import module of ArcGIS Online does not currently support. A simple example would be: https://SOURCE.ORG/tiles/{z}/{x}/{-y}.png when tiles are inverted on y axis (regular issue on some regional providers especially). It would be very useful to have this flexibility on tiles syntax.
True, TMS should indeed be replaced by WMTS as OCG standard when possible. Yet, as stated by another commmunity user: "the xyz standard is (still) in use by Google, OSM, and Mapbox, as well as a number of regional providers. We cannot always control what map services we are delivered by our input data sources". (source)