A relatively recent example of this rare breed of instruments - http://www.harmoniumnet.nl/Lenter-Orgelharmonium.html
I know of around half-a-dozen others, but have only seen an amateur-built (and currently unplayable) example in the reed organ museum at Saltaire.
The biggest problem that I can see is the shift of pitch of the pipes with temperature changes (electronic/pipe hybrids suffer from the same problem). The sound clip mentioned on the web page is also worth listening to. I think the CD is one for my "wish list!". Every Blessing