The D. capensis, S. flava, and U. sandersonii have been growing in this set-up for almost a year, the P. primuliflora for six months. As with any potted arrangement and the fact that many of these plants are still immature, yes they will eventually need to be repotted and/or separated as they outgrow their current home. But, this arrangement saved these plants from certain death: all of these plants were headed for the compost bin as they were "weeded" from other pots. Some people prefer to meticulously label and organize all their pots single file in rows. That's fine. I on the other hand prefer to group plants in more natural settings that compliment the plants. Plain plastic pots serve their purpose but aesthetically are visually boring. I like to break up the monotany every now and again by experimenting.
Ever seen a beautifully landscaped terrarium, ie. planted directly in soil substrate? From a functional stand point it can be a challenge to maintain due to different medium and cultural requirements, but doesn't it please the eye? I am just trying to illustrate that form and function can co-exist together. Endparenthesis, to answer your question, yes a VFT would complete the package, but the fact that the pot is undrained and the water table fluctuats from time to time, the rhizome would likely rot if or when submerged for any length of time.
Thanks for all the comments. I will continue to experiment with other combinations and encourage others to follow suit. Just make sure you have some experience or at the least extras (plants of course!).