UnForm currently supports pcl6 printers with certain limitations. You can get this support by configuring GhostScript in the [drivers] section of uf80d.ini. There are two entries in that section that allow pcl6 output, by specifying -p pcl6 or -p pcl6c (color) on the uf80c command line.
The limitations are that no printer control features for tray, bin, or duplex are available. This is because unform creates a PDF work file, then uses Ghostscript to produce the pcl6 output from that.
We do not plan to develop a specific unform driver for pcl6. We do have a new driver planned for unform 9, but it is for html5, not a printer language. We have found that PostScript is supported on a very large number of business-class printers, much more so than several years go, so there is less and less need for a pcl6 driver. The pcl6 language is entirely different from pcl5 (they share nothing, not a single command sequence), so developing a new driver would be a major effort, and we don't see much need beyond what you can already do via GhostScript or PostScript.