Totally agree, once the ol' Uniglide cog(s) are worn out, simply move on. Or mothball it now for a collectible model of bike that you want to keep it OEM specific.
I have found and stumbled upon abandoned 7-spd HG freehub bodies that I have salvaged for swapping Uniglide 105 and 600 freehubs. A few will take both UG and HG cassettes. So, I'm all set, I'm sure others have done similarly.