Not an expert but as a layman I can tell that plants kept inside a library is likely to increase the humidity which might have adverse effect on the books, microfiche and archival material
My opinion Positive, It is beneficial and bring pleasant feel to the person when introduced in indoor. Only need a little natural light and limited occupancy based on your room space.
From the aesthetic point of view, flowers in rooms always make a space more elegant, more quiet and peaceful. We grow flowers at home (even 1.5 m small palms). So, in my opinion. yes, flowers in libraries are fine.
Keeping plants or forming bio-wall inside the library can create both positive and negative effect. Sometimes it can create an aesthetic as well as joyful moment. But planting more plants can create humid condition which may have adverse effects on books. You are advised to plant succulents, cactus, fern etc. which need less water and sunlight to grow. They even transpires less to create humid condition.