In the UK Relient Robins and the Original Morgan three wheelers had a reputation for tipping over when cornering, often with fatal results. Many, many, years ago the original Top Gear team rolled a Robin several times, which was fun to watch. Think about the Moose avoidence test, and avoiding accidents at speed on freeways. 3 wheeled cars are less stable than 4 wheeled cars. Augmenting stabilty with electronics can go wrong - see 737 Max. Perhaps castors on rear corners, as on some RVs with long rear overhangs.
An important segment of initial purchasers will include rich old men trying to re-live their youth and show off their greeness. Get some overweight geriatrics to test the getting in and out. The rest of the world is going to higher SUVs, which are easier to get into.
Opening windows are required at toll booths, ATMs, entrances to gated comunities, talking to police after traffic stops, etc
Federally mandated heights for bumpers/fenders?
Low car may not be seen in some traffic situations. Think flags on recumbent cycles.
Front and rear streamlined fenders should be (part) removable for driving in slush/snow/mud. Can slush / snow jam up inside fenders and stop the wheel rotating?
The solar panels wil get dirty when parked. Consider a purpose made cleaning tool. Think brolly in door of RR.
Overall the concept is logical, attractive, and excellent. An excellent start.