As items (iii) (although it incorrectly says "(ii)") and (iv) of the caption of figure 1, are reasonable considerations.
There is also the consideration of faulty displays, in case a segment stops working (although you can mitigate this problem somewhat, by adding a test switch to light up all of the segments).
About decimals, one possibility (depending on the application) is to require a fixed position for the decimal point and add a wider gap between the digits at that position, which improves the clarity.
They also mention, "the user cannot see the difference between entering zero, or entering zero then decimal point". This is a problem on many hand-held calculators but it is easy to avoid, by not displaying the decimal point unless it has been entered explicitly (or if the result is being displayed).
Upsidedown (also mentioned in the article) is also a reasonable consideration, although there are ways to mitigate that too.
This would allow for failure detection without the user having to explicitly press a test button and look for any misbehaving segments. You can't do this as easily (if at all) with LCD or OLED.
Also, fairly trivial to detect if a display has a segment out and throw a fault if needed. It's also not likely you burn out a whole segment at once if you have it wired up with that in mind.
It’s almost like that is what electronic design means, creating a curcuit that works is perhaps the easiest part. Choosing all the parameters for the parts to be used and keeping it under the target cost is the hardest!