There is no need to file a feature request for the two things you've mentioned.
When you look at the HTML Whitelist, there is a note near the top:All elements allow style ... title ...
Since iframe is a supported tag, it supports the title. You'll need to view the HTML to fix it, but you're probably viewing HTML if you're inserting your own iframe anyway.
Table captions should be aligned using CSS through the style attribute. The align attribute has been deprecated since HTML 4.01 and obsolete since HTML 5. Once again, style is allowed on all supported tags. You can include a caption within a table, so to make it left aligned, you would do something like this right after the opening table tag.
<caption style="text-align:left;">Summary Statistics</caption>
Again, you'll need to edit HTML to set the style. You cannot use the left, right, or center alignment buttons.
Btw, the align tag for a table cell suffered the same fate and is no longer guaranteed to work.
Asking for a smoother experience or easier to apply within the Rich Content Editor might be a feature request, but asking that they be added to the WhiteList isn't going to do any good because they are already supported.
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