Version 6 was an innovative design that may be revisited in the future. In place of lead screws, belts or rack and pinon, we have here a Roller Pinion system.
Version 6’s roller pinon turned out to be inconvenient with the limited placement of the drive system. For practical purposes it was discovered (during the design) that the drive system took up a lot of valuable space. Since one of the founding design goals is to have a high build volume to foot print ratio, this design was grudgingly shelved in favour of belt based ones. It may however make a come back in some form or fashion.