I’m in agreement that developer-centric syntax is best be avoided, or should be a last resort. Presentational information should be avoided in HTML and Markdown too. Image alignments are definitely presentational information that may differ across different websites and applications. There were some arguments put forward earlier in this topic that extra image information (such as alignment) sometimes needs to be explicitly defined. Hence the proposal for consistent attribute syntax. This would at least avoid requiring presentational information (you could give the class name a more semantic meaning), but it isn’t ideal.
Such features have been requested, however I do question their necessity. There are other ways of defining image properties. These could be in a predefined pattern for image alignments defined by the application. Or pulled from a separate place (a YAML file or a database table), keeping the Markdown document clean of additional properties. Perhaps another markup language could contain presentational information and applied to images mentioned in a Markdown document after the draft is complete. Separation of concerns between the author and “document formatter”.