While the real Paula can only join two 8-bit channels to be one 14-bit channel, we could give it a true 16-bit channel.
Interesting idea. I think this could be achieved without any need for additional software support.
You need some simple logic to detect a condition where channels from single side have the same sampling frequency (rate) and volume set to either 64 and 1 or 1 and 64. See here for details:
http://aminet.net/package/mus/misc/Pro14bitbetWhen the condition is met you can then take the two different 8-bit components and produce a true 16-bit data out of it.
This way it would work with manual tricks such as descibed in the Pro14bitbet and with the 14-bit noteplayers available for various player apps (such as
http://aminet.net/package/mus/play/Deli14BitGenie). As a bonus you'd get 16-bit paula AHI for free (paula.audio supports the 14-bit mode).