The setup I've been daydreaming about lately I'm not sure is really possible, but it's basically a mangrove in a large glass bulb where the roots spread across and fill out the inside of the bulb, and the tree has some nice growth growing outside of it as well. Maybe imagine these images combined:
The end result would be a somewhat bonsaied mangrove that is then impossible to get out of the bulb, as the roots would have grown in and spread out wider than the opening. I would then add an aquasoil capped with gravel to the bottom and just do dwarf hair grass and littorella uniflora to carpet it, and maybe have a floating stem plant at the top of the roots. For stocking it would depend if I end up making this brackish or freshwater but it would be some kind of shrimp. Rudolph if brackish and maybe some caridina if fresh. Anyways, I've started growing the mangrove in mud and have the bulb as well. I completely understand that this might not work and if it does, it will take years and likely still turn out differently than I expect. Just what I've been daydreaming about.