While I agree it would be “cool” for Servoy to expose those extra layers so you can build your own custom front-ends on any framework you want, I disagree that its what they should be focusing on. Servoy is about RAD. As with most RAD tools, the deployment frameworks are chosen for you by the RAD tool. Folks that know enough to write their own custom front-ends in the latest/coolest frameworks aren’t really Servoy’s target customer. There are few that would really use it. So, yes, it would be cool, but at what cost, and who would really use it?
The .frm/.html thing is quite annoying (at first). As a developer, I would prefer to edit the HTML of my front end manually, not with a WYSIWYG form designer. However, Servoy stores metadata information about the form design in a JSON structure in the .frm files, so it just isn’t possible. While it is annoying, I get why they do it. If you were an ISV that decided on Servoy many years ago, you had a nice RAD tool to build Java Web Start apps (smart client). Then the web came along, and they gave you Wicket (web client). Then the web 2.0 came along, and now you get AngularJS (ng client). As an ISV, Servoy is future-proofing for you. You only had to build your app once, and Servoy made it work as new technologies came out. Not a lot of tools have successfully pulled that off, but Servoy, to their credit, has done a great job of that!
Should they make it so you can deploy on any framework you want…sure, that would be cool, but its not really why people choose Servoy…IMHO.