It's more mechanical than anything. A short scale length will feel different for sure. Roberto (who started a thread about
balance of 6-string Spoiler body basses, has both long and medium scale basses. I'm sure his thoughts would be valuable for your consideration, Alain.
Scale length is a difficult decision if you don't have references. Try this out: put a B string on your Spoiler bass - don't worry about intonation or set up. What you want to determine is does the sound or feel of the string bother you? If is doesn't, you can be confident in your decision for a medium scale. If it does bother you, then you'll know to steer clear from an expensive mistake.
Let me know what you find out.
Another big issue is the width of the neck. Just because there are 6 strings, doesn't mean you have to have a huge neck width, especially down at the nut.
Strings are an issue, but regardless if you use medium or long scale strings, the mechanical action will be the same - the vibrating length of the string doesn't change. Also, many medium scale strings are too short for our medium scale basses because the bridge and tailpiece are separated. D'Addario Chromes come to mind, most Alembic players buy their extra-long scale for their 34 scale basses. Best is to specify the strings you want to use, then we can figure out if they can be used with yoru specifications before we build the bass.