Results in the list shown in your example. This has some obvious downsides as far as readability in the editor, however.
Perhaps a syntax for lettered lists could be added in a non-intrusive manner.
EDIT: Manually changing the list marker in the first example works in the preview, but the Editor offers no help in continuing to build the list (i.e. the list markers are not formatted, and a carriage return does not generate a new list marker as it would when editing a first-level list). Obsidian does support this, as long as you’ve completed your HTML list first (added last </ol> above)
When making ordered lists Obsidian will successfully recognise that a set of instructions should be successively labelled as ‘1) [Some text] \r\n 2) [More text]’ etc. and will be displayed as ‘1. [Some Text]\r\n 2. [More text]’. This does not apply when creating a sub-set of an instruction using alphabetic characters. I.e., Typing ‘a) [Some text] \r\n’ does not result in the new line having ‘b)’ ready for the next sub-instruction or the preview editor recognising that this is a sub-list.
Add in the use of alphabetic lists to the numbered list functionality.