Here is what the General Instruction of the Divine Office says about hymns:
« A very ancient tradition gives hymns the place in the office that they still retain. By their mystical and poetic character they are specifically designed for God's praise. But they also are an element for the people; in fact more often than the other parts of the office the hymns bring out the proper theme of individual hours or feasts and incline and draw the spirit to a devout celebration. The beauty of their language often adds to this power. Furthermore, in the office hymns are the main poetic element created by the Church » (173)
The liturgical reform precisely allowed the writing of new hymns and that is the reason why the « Commission Francophone Cistercienne » (CFC) got started into writing, together with other authors.
For example, Brother Paul has composed hymns and we sing some of them at the office: