Many thanks to Martyn Little of acejets.co.uk for lending me a Weatronic JR standard adapter.
I have been doing bench testing of it in a Frsky Taranis, and it works. The Taranis, as well as having its own 16 channel Frsky transmission, has a JR module slot to accept any brand transmission system in a standard JR module and can be configured to send from 8 to 16 channels to it.
David Gladwin let me try a Weatronic JR12x adapter but that didn't work.

I have a DV3 module which only recognises up to 12 channels so it worked with the Taranis set anywhere between 8 and 12 channels, but stopped working above 12 channels. I expect the DV4 module would recognise the Taranis up to 16 channels.

In most cases 12 channels is enough since so much can be done on the 12-22 Rx. Given the awful delays to the BAT60, surely Wea would have been much better to initially make a straightforward Tx and get it out on sale, relying on the superb Rx to do much of the work?

The advantage to Taranis is its fantastic OpenTx firmware which is very probably the best, most powerful, most flexible Tx firmware available today. It also helps that it is incredibly low price. The reason I will not use it with my jets is that I do not trust Frsky receivers yet, looking closely at them I am not wholly convinced that they are of sturdy enough construction. I haven't got a problem with using the Taranis.

However the disadvantage would seem to be the refresh rate. With my Multiplex 4000 in 12 channel mode, Giga Control shows it providing 40 source frames per second to the Wea module. GC shows the Taranis in 12 channel mode providing 32 source frames per second. By comparison the old PPM standard is about 50 frames per second for 8 channels. Having said that, I could not notice any difference of the model's reaction when I moved the Taranis's sticks. In 12 channel mode the Mpx 4000 always seemed to have a tiny delay which we attributed to the speed of processing all its program, it was designed in the early 1990s so its hardware is from that era. I expect Taranis to be much faster at processing the signal than the old Mpx 4000 so that may be compensating for the slightly slower data rate. I expect true 2.4Ghz systems to be much faster since they are not choked by having to use the the old PPM data frames, although you end up in the debate about can anyone notice it anyway unless flying extreme helis etc.

The Taranis is basically the old JR9303 case but I don't think Wea makes an aerial mounting to fit the 2.4ghz aerial socket on the Taranis, so it would probably need a user-made item.

I would be interested to hear from anyone who has a JR, Graupner or Futaba Tx that can run 12 channels with Wea, what source frame rate Giga Control says they are getting in 12 channel mode.