The identification of a letter would be improved when its baseline is perfectly clear. The small g looks similar to 9, depending on font, or compare COPTIC CAPITAL LETTER FEI Ϥ with COPTIC SMALL LETTER FEI ϥ. Showing the baseline in the preview would be beneficial for clear identification.
Any implementation would have challenges--font would have to be parsed for its base line and positioned accordingly. Believe we currently just scale the font and center based on the fonts metric.
The baseline would need to be unobtrusive. And guess while parsing for baseline, could also determine width/ascender/descender/leading and show those as well. The dialog would need a toggle for any of these as in truth the majority of users do not need any of the hinting to recognize the character--including showing the baseline.
*** This bug has been marked as a duplicate of bug 90848 ***