Given that I am no Bernard of Clairvaux, I do not write Sermons, I write Homilies.
The starting point is not an individual text of scripture, but the connection/collection of several scriptural texts for a given day within a particular season of the Church Year.
The guide should give first place to the Lectionary, allowing one to choose the date/feast, as on the home page.
It should next show the Missal texts for the day.
A search of all homily aids indexed to the Lectionary would be one of the sections in teh guide.
The real complexity would be triggering searches of Commentaries, Sermons, the Catechism, Church Documents, Church Fathers, Media, Themes, Illustrations based on any of the three or four scriptural texts allocated to the day/feast.