It's a very interesting site, so thanks for sharing.
The problem of course isn't the lack of brackish (or even fully marine) plants, but the fact relatively few of them are suited to aquarium life. If you get a chance to read 'Dynamic Aquaria' you'll see lots of microcosms and mesocosms built around brackish water conditions, filled with things like herbs, sedges, reeds and even small trees. But almost all of these need intense lighting and deep substrates.
Many of the aquarium plants we value come from shallow streams where they live in partial shade underneath the rainforest canopy. For the most part, brackish water habitats are either mangroves or open marshes, and the diversity of small, slow-growing, low-light plants just isn't that high.
Still, people have kept mangroves, and if those can be grown, then I dare say some of these other brackish water plants are worth trying.
Cheers, Neale