[werk_ag]

Ok, maybe I have meant "data that could be used by weather station software"

Ideally I think the hardware should be software agnostic and not dependent upon a singe specific application...

...I suggest, the popular Weather Display.

I agree with that. WeatherDuino Pro2 already works with Weather Display, I haven't fully tested it with Weather Display because I don't like the user interface, also configuration is a mess with tons of options.

With Cumulus the source is closed and even with the new version the author does not seem to have a clear idea of where he is going, apart from planning to start charging for it.

I think he knows where he wants to go! Steve is a great person, even being alone (he is not alone) he provides a great support for all users, even those that never donated a cent.

Open Source solutions such as WeeWX give more warranties of continuity

As you may know I'm a fan of Open Source software. WeatherDuino Pro2 is open Source software.
Relatively to WeeWX, maybe I'm wrong but info about how to install and use it, is far far away from the info available for Cumulus. At least is not so organized.
I'm not a Linux expert, and to be honest I have already tried to install WeeWX, but without success... needs this, needs that... on the other hand, I managed to make the CumulusMX run on a PI (also Linux), at my second try.
WeeWX seems to be more suitable for Linux software experts, and I belive that most of the people that have weather stations, like me, don't have the skills to work with WeeWX.

Provided the Davis protocol emulation is close enough to the original it ought to work with all apps, including for that matter

This may not be totally true, because it also depends on how the protocol is implemented on the weather software part. As an example, in the Davis emulation implemented in the WeatherDuino Pro2, some things don't work in Cumulus1, but works in CumulusMX, those "things" also work in Weather Display, and may even work with WeeWX, who knows .