Due to the highly customized nature of the OSMC keymap making the home button fully dedicated requires a bit more keymapping than just that. You could turn off the OSMC keymap at settings > system > input > peripherals, which would allow for less mappings that needed to be overridden (you would probably still need to dig through keyboard.xml to see if there is other window specific mappings for that key) or use the following keymap in your userdata (this is actually in my long-press keymap guide at the end)…
<keymap>
<global>
<keyboard>
<escape>CECActivateSource</escape>
<escape mod="longpress">CECStandby</escape>
</keyboard>
</global>
<FullscreenVideo>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</FullscreenVideo>
<FullscreenGame>
<keyboard>
<escape/>
</keyboard>
</FullscreenGame>
<Visualisation>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</Visualisation>
<MusicOSD>
<keyboard>
<escape/>
</keyboard>
</MusicOSD>
<slideshow>
<keyboard>
<escape/>
</keyboard>
</slideshow>
<VideoOSD>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</VideoOSD>
<VideoMenu>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</VideoMenu>
<VideoBookmarks>
<keyboard>
<escape/>
</keyboard>
</VideoBookmarks>
<Videos>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</Videos>
<VideoPlaylist>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</VideoPlaylist>
<MusicInformation>
<keyboard>
<escape/>
</keyboard>
</MusicInformation>
<MusicPlaylist>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</MusicPlaylist>
<SongInformation>
<keyboard>
<escape/>
</keyboard>
</SongInformation>
<MovieInformation>
<keyboard>
<escape/>
</keyboard>
</MovieInformation>
<PictureInfo>
<keyboard>
<escape/>
</keyboard>
</PictureInfo>
<PVROSDChannels>
<keyboard>
<escape/>
</keyboard>
</PVROSDChannels>
<PVRChannelGuide>
<keyboard>
<escape/>
</keyboard>
</PVRChannelGuide>
<AddonInformation>
<keyboard>
<escape/>
</keyboard>
</AddonInformation>
<yesnodialog>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</yesnodialog>
<selectdialog>
<keyboard>
<escape/>
</keyboard>
</selectdialog>
<contextmenu>
<keyboard>
<escape/>
</keyboard>
</contextmenu>
<addonsettings>
<keyboard>
<escape/>
</keyboard>
</addonsettings>
<addonbrowser>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</addonbrowser>
<filemanager>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</filemanager>
<interfacesettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</interfacesettings>
<systeminfo>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</systeminfo>
<eventlog>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</eventlog>
<playersettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</playersettings>
<mediasettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</mediasettings>
<pvrsettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</pvrsettings>
<servicesettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</servicesettings>
<gamesettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</gamesettings>
<profiles>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</profiles>
<systemsettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</systemsettings>
<music>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</music>
<pictures>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</pictures>
<skinsettings>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</skinsettings>
<musicplaylisteditor>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</musicplaylisteditor>
<games>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</games>
<programs>
<keyboard>
<escape/>
<escape mod="longpress"/>
</keyboard>
</programs>
</keymap>