I personally do not like reading capitalized content - it makes it harder/slower and "screams" at me. Soncino made an editorial choice, possibly in a time where italics or other fonts weren't as easy to use or as common as today, and that choice feels outdated today.
As such I would much prefer to lower-capitalize the text quoted. But it might just be me.
In my opinion (and others', as shown in the comments on the question), the Jewish date would be unclear to many site visitors. Arguably, one way around that is to display both the Gregorian-calendar and the Jewish dates. But I think the technical difficulties are insurmountable, or nearly:
Date issues: The Jewish date changes at sunset, which time varies ...
The superscript is done with <sup>insert number</sup> which renders as insert number.
(For future reference, if you have an example post where a particular format was used, you can use the edit function on that post to see the underlying formatting.)
Thanks to (I think) Isaac Moses who was the one that showed me how to do this when I was getting ...
What is the current state of RTL on MY?
There is effectively no support for RTL on MY. There are workarounds, which all are inclusions of various characters via HTML entities.
How will SE's plans affect MY?
It seems that they won't, since CommonMark allows inclusion of HTML entities.
I don't care much either way, but if you do change it please note as much (eg. "reformatted by me" or "changed to sentence case" or something like that). And come to think of it I support adding the "capitals in original" note for clarity if you don't change it. So in short, whatever you do, leave a note.
I agree with mbloch's answer here that the capitalized text is harder to read and is likely an artifact of the typography readily available to Soncino Press. But I'll go further and say that if you substitute boldfacing for capitalization then you needn't even note the difference in an editorial note, since boldfacing is the same as what they intended by the ...