@samabbott replied:
Agree this is a big issue though I am not sure how your suggestion helps lower the barriers for entry as new contributors would still not be able to add model features (as they would just be adding UI for those features?).
Yes exactly. I think this would be great if someone did but as below so much effort (see below)
I agree a brms like model generator could be the way to go but to be honest I am not sure a PPL agnostic front-end is less work/learning than just making people learn a new language (i.e. our Julia project 
).
Do you have an example from other fields of the kind of domain specific tool you are thinking about existing?
In my head what you are proposing is a R specific PPL that then under the hood maps to other PPls and contains epi specific functionality. That sound very very hard and high effort to me? What happens if someone just does this mapping from say stan to whatever the new hotness is?
I think the version of this that remains focussed on stan (maybe only for now) is very doable though.
(it remains the responsibility of the developer to implement the model correctly and to reject representations that your stan model cannot implement).
I think this is a separate issue and highlights the problem that I think most of the issue lies in developer time/skill as people (myself included) don’t implement the details correctly. If we had a really nice user interface across lots of still wrong packages that seems like a bad use of effort?
Given that most/all of the currently available tools that exist has fundamental flaws to their infra it seems like we should fix those (by ideally pooling resource) before we worry hugely about a extremely consistent UI. Especially as currently many/most users are relatively specialised/motivated and so can navigate maybe clunky UIs?