[Sony Ericsson XPERIA X10 Mini] porcupineadvocate:
all right, it's done

All right, I got the bar to disappear.

I gave up on finesse and simply rewrote all the layout_height entries to 0.0px in qwerty_statusbar.xml, thus giving this:

<?xml version="1.0" encoding="UTF-8"?>
<RelativeLayout android:orientation="horizontal" android:id="@id/qwerty_statusbar_layout" android:background="#004" android:paddingLeft="0.0px" android:paddingTop="0.0px" android:paddingRight="0.0px" android:paddingBottom="0.0px" android:layout_width="fill_parent" android:layout_height="0.0px" android:layout_alignParentBottom="true"
xmlns:android="http://schemas.android.com/apk/res/android">
<Button android:id="@id/qwerty_hide_button" android:padding="0.0px" android:layout_width="1.0px" android:layout_height="0.0px" android:layout_marginTop="0.0px" android:drawableLeft="@drawable/general_button_close_dialog_nobg" android:drawablePadding="0.0px" android:layout_alignParentRight="true" style="\?style_general_button" />
<Button android:id="@id/qwerty_settings_button" android:layout_width="1.0px" android:layout_height="0.0px" android:layout_alignParentLeft="true" android:layout_centerVertical="true" style="\?style_general_button" />
<RelativeLayout android:orientation="horizontal" android:layout_width="wrap_content" android:layout_height="0.0px" android:layout_toLeftOf="@id/qwerty_hide_button" android:layout_centerInParent="true">
<TextView android:gravity="center_horizontal" android:id="@id/primary_info_text" android:background="#004" android:paddingLeft="0.0px" android:paddingTop="0.0px" android:paddingRight="0.0px" android:visibility="gone" android:layout_width="wrap_content" android:layout_height="0.0px" android:layout_marginRight="0.0px" android:maxWidth="60.0px" android:singleLine="true" android:layout_toLeftOf="@id/secondary_info_text" style="\@style/SuquashiTextAppearanceSmall" />
<TextView android:gravity="center_horizontal" android:id="@id/secondary_info_text" android:background="#004" android:paddingLeft="0.0px" android:paddingTop="0.0px" android:paddingRight="0.0px" android:visibility="gone" android:layout_width="wrap_content" android:layout_height="0.0px" android:layout_marginRight="0.0px" android:maxWidth="40.0px" android:singleLine="true" android:layout_toLeftOf="@id/status_icon" style="\@style/SuquashiTextAppearanceSmall" />
<ImageView android:gravity="center_horizontal" android:id="@id/status_icon" android:background="#004" android:layout_width="wrap_content" android:layout_height="0.0px" android:layout_marginRight="0.0px" android:src="@drawable/textinput_bar_status_icon" android:layout_alignParentRight="true" android:layout_centerVertical="true" />
</RelativeLayout>
</RelativeLayout>

So the bar no longer appears. It seems to work fine, the SYM key summons the symbols menu; the bar just never appears. Correspondingly, there is no indication of the shift/bluesquare keys, but I never paid attention to those anyway. There is also no way to change languages in this mode; you'll have to switch to Portrait and use the soft keyboard to change language.

Screenshots:

Yes, there's a little line just below the results pane in the screenshot. I think it's just an artifact of the results pane. I just tested it in the default Android web browser; typing into the address bar doesn't resize the window as it used to (the SYM key still works fine, though!).