I will start adding here ideas for refactors. Those would become Jira tickets later:
Stop using C flavours of standard libraries (i.e. replace assert.h with cassert, stdlib.h with cstdlib, etc).
Provide an alternate logging implementation in case PmLog is not available, and replace usage of printf for error handling.
Find geometry types. As we'll drop Qt, we need replacement for things like QSize and QRect. We cannot use Chrome alternates either.
Move WebOSWebView specific implementation from src/platform/webengine to src/platform/webengine/webos_webview. Only use webos webview headers from there (previous step to getting again multiple web engines support). Similar refactor could be needed for window implementation, as it is based on the existing abstractions and wayland implementation in webos webview.
Major
Breakdown refactors needed in WAM to properly abstract webOS, AGL and desktop.
This should, at least, include refactoring the system bus in WAM so it can use AGL binder on WAM and Luna bus on WebOS (and maybe dbus on desktop).