Oh.. so the art/assets pipeline is pretty much dictated by the internal teams. But feel free to use the engine and explain on Defold forums of the good and the bad. We'll be happy to listen.
The asset pipeline is not as customizable as one could wish for in it's current form, but something that will change with the upcoming new editor. In honesty, we haven't had a lot of requests in this regard in-house yet, but if this is something that is highly requested by indie users we will surely look into this.
(Hold tight, going into a bit of a tangent below.)
We put a lot of effort into performance, keeping the binaries small and having fast development iteration.
One very nifty thing is that the build/pipeline can be run as command line command, without even opening the editor, which enables you to setup your own build command in Sublime Text or on a build bot for example... (I have something like this at home where I can code in Sublime, hit Ctrl+B and it will build with the same code as the editor and automatically launch the game, all from inside my favorite code editor. Just imagine how sweet this will be when the pipeline/engine is a bit more extendable. :))
Yet another cool thing of course is being able to hot reloading resources while the game is running, also tying into the fast development iterations.
Hope this at least answers some of your questions. :)
Defold seems like a nice idea. As with any games engine it's never about the quality of the engine but the asset pipeline you put in front of it (see Unreal engine for a grade A example of this). I didn't see much talk about the asset pipeline, I see people from King are around, anyone care to comment?