indeed, that thing'll be an absolute pain in the butt to clean. especially if its mounted flush to the wall at eye-level (which would be the most attractive although impractical way to mount such a thing.)
remember, smaller tanks need frequent water changes. anything under 30 needs at MINIMUM a weekly 15% change and that's only if it isn't overstocked and underplanted. since a 30g tank would weigh some 250 POUNDS, that "plasma tank" is probably not anywhere close to that large. it probably is in the 8g range and would definitely need a weekly clean.
but cleaning concerns aside, there aren't too many fish suited for a 5 inch wide tank. most small fish are fairly skittish, need plenty of cover, and prefer lots of companions. the only thing that i can think of that might be even close to suitable is a school of 5-8 pygmy cories. pygmy cories (c. habrosus, i believe) stay under an inch in length, don't produce much waste, are actually mid-level swimmers and should do pretty good in a small school. they aren't very flashy, but like most cories are quite enchanting to watch.
although not many people want to shell out for this, you could have a fantastic plant-only tank. a plant-only tank (as far as i know) wouldn't require frequent water changes but would need regular fertilization and a CO2 system. it could easily be more expensive than owning fish, but after the initial setup of some automated systems, a plant-only tank wouldn't require frequent maintenance. a well-designed planted tank is often more eye-catching and impressive than the typical community tank simply because it's far more rare. you could possibly even include some of the fancier small freshwater invertebrate (such as bumblebee, cherry or amano shrimp) if you didn't mind incorporating the extra maintenace.
if you decide to get the "plasma tank", whatever you decide to do should DEFINATELY incorporate a high level of real planting. its my opinion that nothing helps control water quality between maintenance periods better than live plants. using live plants is not an alternative to weekly water changes, but it does help improve the effectiveness of you maintenance efforts.