I look it once upon a time. It's dependency with third party libs (GR32), complicated and unfinished, to finish it is not real for me.
As far as I can see there are ifdefs to disable graphics32, but I'm inclined to take your word at this point.
Required, but not done:
-Prevent stealing focus from the main form
As I understand, last point is impossible made by LCL, only platform specific methods.
actually it might be the opposite, In order for an unfocused "popup" window to work, the form needs to have a "popup form" property to forward keyboard events to it and continue processing keys that are not processed by it, The "popup form" must have a "parent form" property to swift its focus to, when it gets it.
As a side note, the FPGUI developer claims that he has a popup form that behaves properly I would suggest to take a look and see if that helps at all.
Looking good so far. I have to download and check it out some time.