Not in the least a realistic solution, but probably the only "ideal" solution would be to have both side and rear entry, as there are use cases for each that are ideal and wouldn't work for the other... Rear entry is great in parking lots (bays? if I understand the UKlish properly

) where the cars are side by side, and even a so called "van accessible" space is chancy due to idiots parking on the cross-hatching. OTOH, parking nose-to-tail along the side of the street is going to be a problem for the rear entry, but probably work well for the side entry....
Used to be a common saying, "Tell me what kind of accident you are going to have, and I'll tell you what sort of protective gear to wear" - the WAV version is "Tell me where you are going to park, and I'll tell you what kind of entry to get..."
Trouble is, I'm likely to encounter both kinds of parking depending where I'm going on a given trip. If going to the local shopping center, I will be in a side by side lot. OTOH, going to a friends house, or heading into Boston, the odds are pretty good that I'll be parallel parking, likely in a space that is only 6" longer than my vehicle...
Of course in the US, the options aren't all that great - far as I know, all the "drive from chair" capable converted vehicles are side entry. This is also the most common choice for any of the converted vehicles. The few rear entry conversions are passenger only, and even then the wheelchair passenger ends up in the back, as the dropped floor doesn't go up as far as the front seats.
ex-Gooserider