> unless the BR-Script3 is a replacement for PostScript, > though I doubt that, but it could mean a BRother printer > specific version of PostScript3 that they have developed.
It indeed is. BR-Script is the name of Brother's own PostScript implementation and should be compatible with standard PostScript drivers. So it could be worth using MorphOS' new printing system with a compatible PPD file to make a BR-Script3-capable printer work with MorphOS. With a printer also compatible with PCL5, this could even work in case BR-Script isn't sufficiently compatible, namely using the new printing system's PCL5 driver.
> or you would probably have to use the TurboPrint (PS) > or GhostScript (GS) capability
For printing PostScript data to a non-PostScript (but PCL-capable) printer via TurboPrint, using GhostScript is a hard requirement. TurboPrint creates the PS: device only in conjunction with GhostScript.