It is definitely possible for a very skilled Chef to implement Landscape into a Manila 2.5 rom. Here is an example for the Sony Xperia!
Rotastrains Blaze v1 [MAnila 2.5 THE FIRST EVER LANDSCAPE SUPPORTED ROM]
Description: This is the first landscape supported manila 2.5 rom.The manila landscape has been made by me.It has windows mobile 6.5. (23016)
Screen Shots:
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