Here is an answer to an earlier similar question, which shows something similar: Sequential Numbers using Drag - #4 by dmitry-grist. In particular, the example document referenced there has an in-group numbering example: Sequential Numbers - Grist.
For this one, you’d set the group manually (or fill in a range with the same group using the ⌘ D / Ctrl + D shortcut), and the incrementing numerical suffix is added automatically.
Still, the original request is different. It is indeed sometimes very convenient to fill in a range with auto-incrementing values. It may not be hard to implement, as long as the interface is simple. Dragging a box is not so simple, but another idea is to select a range, press that existing ⌘ D / Ctrl + D shortcut, and then ask the user with a popup if they want to fill in the range with the values in the top cell, or an arithmetic sequence based on the top two cells (when both options seem possible). If that sounds useful, opening a github issue is a good way to go.