'Thinking about it' might just mean referring the question to the management at my place of worship, but does anyone here have any thoughts to share? It seems to me it's not a shocking request. There's a deep seated love of devotions to Our Lady that don't have an outlet these days, and the people asking are not arch-traditionalists on the fringes, just ordinary parishioners. And given that the 'recessional hymn' is hardly integral to the rite, does it matter if it wanders off topic (if that's how you view what is being asked for)?
Ideally we'd be singing a hymn of thanksgiving at the end of the Communion rite, rather than a final hymn, and ideally the church would be thronging with people for afternoon devotions at which they could sing about crowning with blossoms, wicked men blaspheming and so forth to their hearts' content. But neither of these things are going to happen in a hurry.
So what should we do? Just bung in a hymn to Our Lady at the end, unexplained? I'd hope to resist that. Flatly refuse to accommodate devotional needs that don't strictly belong in the Mass? That would feel a bit like riding roughshod over pastoral need. Catechise the faithful away from old ways? Rather you than me. Or find some way to incorporate Marian devotions (in the best spirit of Lumen Gentium, naturally

What do you reckon? And I wonder what the Directory on Popular Piety and the Liturgy says? I'll have to go and look it up.
M.