Since Pope Francis' "exhortation" is the post-synodal exhortation for last Fall's Synod on the New Evangelization, convened by Pope Benedict XVI, it is necessary to point out that deacons didn't receive much consideration during the Synod. Hence, it is hardly surprising deacons don't receive much of a mention in the Holy Father's post-synodal Apostolic Exhortation.
It also bears noting, again, as I did at time of last Fall's Synod, that it was the Anglican Bishop of Sheffield, England, Dr. Steven Croft, who mentioned deacons during his brief intervention, during which he said, "Finally, who will be the new evangelisers? I commend further reflection on diakonia and the ministry of deacons." A commendation that largely seems to have fallen on deaf ears.
Deacons were mentioned in the Propositions submitted to the Holy Father at the end of the Synod's deliberations, towards the end of Proposition 49 to be exact: "The Synod recognizes and encourages the work of deacons whose ministry provides the Church great service. Ongoing formation programs within the diocese should also be available for deacons."
Looking at the Lineamenta, or, preparatory document, for the Synod on the New Evangelization, there are 30 questions posed in section 22. Number thirty is: "How has the ministry of the permanent deaconate (sic) been included in the Church's mandate to evangelize?" This is the only place where deacons or the diaconate is mentioned. It's not an open question. Deacons, by the very nature of the ministry of our order, are evangelists!