I'm pretty sure part of the class system that socialists are trying to get rid of include the monarchy. I think setting them up as an ideal "first citizen'" or elder would just be aestart of the class system as it would be someone outside if the working class who is being pointed to as the arbiter of what to do, not the working class themself. And the former monarch would not be happy seeing their residences, their family jewels and other luxuries seized and then auctioned off or repurposed into housing for the homeless or a soup kitchen. Counterevolutions would try to make them into a monarch again and undo your revolution.
Even if this wasn't self contradictory, the monarchy usually doesn't know everything. Queen Elizabeth II is great but she gets her advice from her ministers and then follows it. Where would this new elder get their advice?